cxl/mem: Return -EFAULT if copy_to_user() fails

The copy_to_user() function returns the number of bytes remaining to be
copied, but we want to return -EFAULT if the copy doesn't complete.

Fixes: b754ffbbc0ee ("cxl/mem: Add basic IOCTL interface")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YC+K3kgzqm20zCWY@mwandaSigned-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/cxl/mem.c

@@ -752,7 +752,10 @@ static int cxl_send_cmd(struct cxl_memdev *cxlmd,
 	if (rc)
 		return rc;
 
-	return copy_to_user(s, &send, sizeof(send));
+	if (copy_to_user(s, &send, sizeof(send)))
+		return -EFAULT;
+
+	return 0;
 }
 
 static long __cxl_memdev_ioctl(struct cxl_memdev *cxlmd, unsigned int cmd,