mtd: Blackfin NFC: fix invalid free in remove()

Since info->mtd isn't dynamically allocated, we shouldn't attempt to
kfree() it.  Otherwise we get random fun corruption when unloading
the driver built as a module.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>