platform/chrome: cros_ec_proto: Fix check_features ret val

The kerneldoc for cros_ec_check_features() states that it returns 1 or 0
depedending on whether a feature is supported or not, but it instead
returns a negative error number in one case, and a non-1 bitmask in
other cases.

Since all call-sites only check for a 1 or 0 return value, update
the function to return boolean values.

Signed-off-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Link: https://lore.kernel.org/r/20210916014632.2662612-1-pmalani@chromium.org