Fix NULL pointer exceptions when platform data is not supplied.

Trace of one exception:
Unable to handle kernel NULL pointer dereference at virtual address 00000008
pgd = c0004000
[00000008] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 2 PID: 1 Comm: swapper/0 Not tainted 3.14.0-12045-gead5dd4687a6-dirty #1628
task: eea80000 ti: eea88000 task.ti: eea88000
PC is at max77693_muic_probe+0x27c/0x528
LR is at regmap_write+0x50/0x60
pc : [<c041d1c8>]    lr : [<c02eba60>]    psr: 20000113
sp : eea89e38  ip : 00000000  fp : c098a834
r10: ee1a5a10  r9 : 00000005  r8 : c098a83c
r7 : 0000000a  r6 : c098a774  r5 : 00000005  r4 : eeb006d0
r3 : c0697bd8  r2 : 00000000  r1 : 00000001  r0 : 00000000
Flags: nzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
Control: 10c5387d  Table: 4000404a  DAC: 00000015
Process swapper/0 (pid: 1, stack limit = 0xeea88240)
Stack: (0xeea89e38 to 0xeea8a000)
9e20:                                                       c08499fc eeb006d0
9e40: 00000000 00000000 c0915f98 00000001 00000000 ee1a5a10 c098a730 c09a88b8
9e60: 00000000 c098a730 c0915f98 00000000 00000000 c02d6aa0 c02d6a88 ee1a5a10
9e80: c0a712c8 c02d54e4 00001204 c0628b00 ee1a5a10 c098a730 ee1a5a44 00000000
9ea0: eea88000 c02d57b4 00000000 c098a730 c02d5728 c02d3a24 ee813e5c eeb9d534
9ec0: c098a730 ee22f700 c097c720 c02d4b14 c08174ec c098a730 00000006 c098a730
9ee0: 00000006 c092fd30 c09b8500 c02d5df8 00000000 c093cbb8 00000006 c0008928
9f00: 000000c3 ef7fc785 00000000 ef7fc794 00000000 c08af968 00000072 eea89f30
9f20: ef7fc85e c065f198 000000c3 c003e87c 00000003 00000000 c092fd3c 00000000
9f40: c08af618 c0826d58 00000006 00000006 c0956f58 c093cbb8 00000006 c092fd30
9f60: c09b8500 000000c3 c092fd3c c08e8510 00000000 c08e8bb0 00000006 00000006
9f80: c08e8510 c0c0c0c0 00000000 c0628fac 00000000 00000000 00000000 00000000
9fa0: 00000000 c0628fb4 00000000 c000f038 00000000 00000000 00000000 00000000
9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
9fe0: 00000000 00000000 00000000 00000000 00000013 00000000 c0c0c0c0 c0c0c0c0
[<c041d1c8>] (max77693_muic_probe) from [<c02d6aa0>] (platform_drv_probe+0x18/0x48)
[<c02d6aa0>] (platform_drv_probe) from [<c02d54e4>] (driver_probe_device+0x140/0x384)
[<c02d54e4>] (driver_probe_device) from [<c02d57b4>] (__driver_attach+0x8c/0x90)
[<c02d57b4>] (__driver_attach) from [<c02d3a24>] (bus_for_each_dev+0x54/0x88)
[<c02d3a24>] (bus_for_each_dev) from [<c02d4b14>] (bus_add_driver+0xe8/0x204)
[<c02d4b14>] (bus_add_driver) from [<c02d5df8>] (driver_register+0x78/0xf4)
[<c02d5df8>] (driver_register) from [<c0008928>] (do_one_initcall+0xc4/0x174)
[<c0008928>] (do_one_initcall) from [<c08e8bb0>] (kernel_init_freeable+0xfc/0x1c8)
[<c08e8bb0>] (kernel_init_freeable) from [<c0628fb4>] (kernel_init+0x8/0xec)
[<c0628fb4>] (kernel_init) from [<c000f038>] (ret_from_fork+0x14/0x3c)
Code: caffffe7 e59d200c e3550001 b3a05001 (e5923008)
---[ end trace 85db969ce011bde7 ]---

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: <stable@vger.kernel.org>
Fixes: 190d7cfc


Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>