When using the ssi-protocol driver with the Nokia N950, the
following error is thrown during modem powered up sequence.

[13852.274993]  port0: SSI error: 0x01
[13852.279205] ssi-protocol ssi-protocol: RX error detected
[13852.284820] ssi-protocol ssi-protocol: Main state: 1
[13852.290069] ssi-protocol ssi-protocol: Recv state: 0
[13852.295288] ssi-protocol ssi-protocol: Send state: 0
[13852.300537] ssi-protocol ssi-protocol: CMT Offline
[13852.305603] ssi-protocol ssi-protocol: Wake test 1
[13852.310638] ssi-protocol ssi-protocol: Data RX id: 0
[13852.315887] ssi-protocol ssi-protocol: Data TX id: 0
[13856.001464] ssi-protocol ssi-protocol: Watchdog trigerred
[13856.007293] ssi-protocol ssi-protocol: Main state: 1
[13856.012542] ssi-protocol ssi-protocol: Recv state: 0
[13856.017761] ssi-protocol ssi-protocol: Send state: 0
[13856.023010] ssi-protocol ssi-protocol: CMT Offline
[13856.028045] ssi-protocol ssi-protocol: Wake test 0
[13856.033111] ssi-protocol ssi-protocol: Data RX id: 0
[13856.038330] ssi-protocol ssi-protocol: Data TX id: 0

This patch fixes the issue by using the handshake setup from
the Nokia N950 kernel. The new handshake sequence also works
with the N900, so there is no need to differentiate between
both modems.

Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Sebastian Reichel <sre@kernel.org>