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/9p/vfs_super.c b/fs/9p/vfs_super.c
index 7b0cd87..10b7d3c 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -155,9 +155,8 @@
 		goto release_sb;
 	}
 
-	root = d_alloc_root(inode);
+	root = d_make_root(inode);
 	if (!root) {
-		iput(inode);
 		retval = -ENOMEM;
 		goto release_sb;
 	}