nfs: testing for null instead of ERR_PTR()

nfs_path() returns an ERR_PTR(), it doesn't return null.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index e016372..f9327bb 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -2657,7 +2657,7 @@
 	devname = nfs_path(path->mnt->mnt_devname,
 			path->mnt->mnt_root, path->dentry,
 			page, PAGE_SIZE);
-	if (devname == NULL)
+	if (IS_ERR(devname))
 		goto out_freepage;
 	tmp = kstrdup(devname, GFP_KERNEL);
 	if (tmp == NULL)