mtd: nand: mxc_nand: mark 'const' properly

mtd: nand: mxc_nand: mark 'const' properly

The values pointed by the pointer are used as read-only.
Also, mtd_device_parse_register() uses 'part_probes[]' as
the second argument which is defined as 'const char * const *types'.
Thus, the 'const' should be moved to be after the '*'.

drivers/mtd/nand/mxc_nand.c:269:25: warning: duplicate const

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>