isdn/diva: fix section mismatch

__exit function is used by both init and exit routines, so it cannot
be marked __init.  (from allyesconfig)

WARNING: drivers/built-in.o(.text+0x9b83cf): Section mismatch: reference to .exit.text: (between 'divasfunc_exit' and 'didd_callback')

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Karsten Keil <kkeil@suse.de>
Acked-by: Armin Schindler <armin@melware.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>