fs/fat/inode.c: fix sb_rdonly() change

Commit bc98a42c ("VFS: Convert sb->s_flags & MS_RDONLY to
sb_rdonly(sb)") converted fat_remount():new_rdonly from a bool to an
int.

However fat_remount() depends upon the compiler's conversion of a
non-zero integer into boolean `true'.

Fix it by switching `new_rdonly' back into a bool.

Link: http://lkml.kernel.org/r/87mv3d5x51.fsf@mail.parknet.co.jp
Fixes: bc98a42c

 ("VFS: Convert sb->s_flags & MS_RDONLY to sb_rdonly(sb)")
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Joe Perches <joe@perches.com>
Cc: David Howells <dhowells@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>