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 <[e-mail]>
Reviewed-by: Orlando Chamberlain <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Hans de Goede <[e-mail]>
Signed-off-by: Hans de Goede <[e-mail]>

drivers/platform/x86/apple-gmux.c

···
 		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;
···
 	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;