platform/chrome: wilco_ec: Provide correct output format to 'h1_gpio' file

Function 'h1_gpio_get' is receiving 'val' parameter of type u64,
this is being passed to 'send_ec_cmd' as type u8, thus, result
is stored in least significant byte. Due to output format,
the whole 'val' value was being displayed when any of the most
significant bytes are different than zero.

This fix will make sure only least significant byte is displayed
regardless of remaining bytes value.

Signed-off-by: Bernardo Perez Priego <bernardo.perez.priego@intel.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>