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: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>