HID: alps: Report an error if we receive invalid data in 't4_read_write_register()'

If the data received is not what is expected, we should return an error.

Otherwise, we return 0 or a positive value which will be interpreted as
success, but '*read_val' has not been updated.

Fixes: 73196ebe ("HID: alps: add support for Alps T4 Touchpad device")
Signed-off-by: NChristophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/hid-alps.c

@@ -219,6 +219,8 @@ static int t4_read_write_register(struct hid_device *hdev, u32 address,
 			goto exit_readbuf;
 		}
 
+		ret = -EINVAL;
+
 		if (*(u32 *)&readbuf[6] != address) {
 			dev_err(&hdev->dev, "read register address error (%x,%x)\n",
 			*(u32 *)&readbuf[6], address);