mtd: fix different address space noise

In mtd_ioctl MEMGETREGIONINFO the region_user_info pointer ur
is cast in __kernel space. This produces a number of sparse warnings
like:

warning: cast removes address space of expression
warning: incorrect type in initializer (different address spaces)
   expected unsigned int const [noderef] <asn:1>*register __p
   got unsigned int *<noident>

Since argp is already a void __user * just use it dirrectly without
the cast and make ur a __user *.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>