fat: fat_notify_change() and check_mode() cleanup

- Rename fat_notify_change() to fat_setattr()
- check_mode() cleanup
- Change layout of code

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>