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

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/squashfs/super.c b/fs/squashfs/super.c
index ecaa2f7..970b116 100644
--- a/fs/squashfs/super.c
+++ b/fs/squashfs/super.c
@@ -316,11 +316,10 @@
 	}
 	insert_inode_hash(root);
 
-	sb->s_root = d_alloc_root(root);
+	sb->s_root = d_make_root(root);
 	if (sb->s_root == NULL) {
 		ERROR("Root inode create failed\n");
 		err = -ENOMEM;
-		iput(root);
 		goto failed_mount;
 	}