Btrfs: kmalloc() doesn't return an ERR_PTR

The error handling was copy and pasted from memdup_user().  It should be
checking for NULL obviously.

Fixes: abccd00f8a ('btrfs: Fix 32/64-bit problem with BTRFS_SET_RECEIVED_SUBVOL ioctl')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ioctl.c

@@ -4553,9 +4553,8 @@ static long btrfs_ioctl_set_received_subvol_32(struct file *file,
 	}
 
 	args64 = kmalloc(sizeof(*args64), GFP_NOFS);
-	if (IS_ERR(args64)) {
-		ret = PTR_ERR(args64);
-		args64 = NULL;
+	if (!args64) {
+		ret = -ENOMEM;
 		goto out;
 	}