Char: sx, fix io unmapping

board->base is increased for CF cards after mapping. Use board->base2
for unmapping the region, since it holds the original/correct address.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>