platform/x86: apple-gmux: return -EFAULT if copy fails

The copy_to/from_user() functions return the number of bytes remaining
to be copied, but we want to return -EFAULT to the user.

Fixes: ce3fef2eb235 ("platform/x86: apple-gmux: add debugfs interface")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Orlando Chamberlain <orlandlch.dev@gmail.com>
Link: https://lore.kernel.org/r/0bdfa8c2-cb22-4bec-8773-584060613043@kili.mountainReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/apple-gmux.c

@@ -694,7 +694,6 @@ static ssize_t gmux_selected_port_data_write(struct file *file,
 		const char __user *userbuf, size_t count, loff_t *ppos)
 {
 	struct apple_gmux_data *gmux_data = file->private_data;
-	int ret;
 
 	if (*ppos)
 		return -EINVAL;
@@ -702,16 +701,16 @@ static ssize_t gmux_selected_port_data_write(struct file *file,
 	if (count == 1) {
 		u8 data;
 
-		ret = copy_from_user(&data, userbuf, 1);
-		if (ret)
-			return ret;
+		if (copy_from_user(&data, userbuf, 1))
+			return -EFAULT;
+
 		gmux_write8(gmux_data, gmux_data->selected_port, data);
 	} else if (count == 4) {
 		u32 data;
 
-		ret = copy_from_user(&data, userbuf, 4);
-		if (ret)
-			return ret;
+		if (copy_from_user(&data, userbuf, 4))
+			return -EFAULT;
+
 		gmux_write32(gmux_data, gmux_data->selected_port, data);
 	} else
 		return -EINVAL;