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/nfs/getroot.c b/fs/nfs/getroot.c
index dcb6154..801d6d8 100644
--- a/fs/nfs/getroot.c
+++ b/fs/nfs/getroot.c
@@ -49,11 +49,9 @@
 {
 	/* The mntroot acts as the dummy root dentry for this superblock */
 	if (sb->s_root == NULL) {
-		sb->s_root = d_alloc_root(inode);
-		if (sb->s_root == NULL) {
-			iput(inode);
+		sb->s_root = d_make_root(inode);
+		if (sb->s_root == NULL)
 			return -ENOMEM;
-		}
 		ihold(inode);
 		/*
 		 * Ensure that this dentry is invisible to d_find_alias().