switch open-coded instances of d_make_root() to new helper

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 86ee272..28bd64d 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -188,30 +188,20 @@
 {
 	struct inode *inode;
 	struct ipc_namespace *ns = data;
-	int error;
 
 	sb->s_blocksize = PAGE_CACHE_SIZE;
 	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
 	sb->s_magic = MQUEUE_MAGIC;
 	sb->s_op = &mqueue_super_ops;
 
-	inode = mqueue_get_inode(sb, ns, S_IFDIR | S_ISVTX | S_IRWXUGO,
-				NULL);
-	if (IS_ERR(inode)) {
-		error = PTR_ERR(inode);
-		goto out;
-	}
+	inode = mqueue_get_inode(sb, ns, S_IFDIR | S_ISVTX | S_IRWXUGO, NULL);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
 
-	sb->s_root = d_alloc_root(inode);
-	if (!sb->s_root) {
-		iput(inode);
-		error = -ENOMEM;
-		goto out;
-	}
-	error = 0;
-
-out:
-	return error;
+	sb->s_root = d_make_root(inode);
+	if (!sb->s_root)
+		return -ENOMEM;
+	return 0;
 }
 
 static struct dentry *mqueue_mount(struct file_system_type *fs_type,