fs/affs/super.c: use affs_set_opt()

Replace direct mount option assignation by affs_set_opt() macro.

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>