remove useless tolower in isofs

Remove useless tolower in isofs

Signed-off-by: dave young <hidave.darkstar@gmail.com>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>