Input: elantech - use all 3 bytes when checking version

Apparently all 3 bytes returned by ETP_FW_VERSION_QUERY are significant
and should be taken into account when matching hardware version/features.

Tested-by: Eric Piel <eric.piel@tremplin-utc.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>