[PATCH] Fix oops in vfs_quotaon_mount()

When quota file specified in mount options did not exist, we tried to
dereference NULL pointer later. Fix it.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>