[MTD] mtdchar.c: Fix regression in MEMGETREGIONINFO ioctl()

The MEMGETREGIONINFO ioctl() in mtdchar.c was clobbering user memory by
overwriting more than intended, due the size of struct mtd_erase_region_info
changing in commit 0ecbc81a ('Support
for auto locking flash on power up').

Fix avoids this by copying struct members one by one with put_user(), as there
is no longer a convenient struct to use the size of as the length argument to
copy_to_user().

Signed-off-by: Zev Weiss <zevweiss@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>