ext2: missing unlock in ext2_quota_write()

The inode->i_mutex should be unlocked.

Found by smatch (http://repo.or.cz/w/smatch.git).  Compile tested.
Signed-off-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NJan Kara <jack@suse.cz>

fs/ext2/super.c

@@ -1395,8 +1395,10 @@ static ssize_t ext2_quota_write(struct super_block *sb, int type,
 		blk++;
 	}
 out:
-	if (len == towrite)
+	if (len == towrite) {
+		mutex_unlock(&inode->i_mutex);
 		return err;
+	}
 	if (inode->i_size < off+len-towrite)
 		i_size_write(inode, off+len-towrite);
 	inode->i_version++;