When write in ext4_quota_write() fails, we have to properly release
i_mutex.  One error path has been missing the unlock...
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>