platform/chrome: cros_ec_proto: return 0 on getting wake mask success

platform/chrome: cros_ec_proto: return 0 on getting wake mask success

cros_ec_get_host_event_wake_mask() used to return value from
send_command() which is number of bytes for input payload on success
(i.e. sizeof(struct ec_response_host_event_mask)).

However, the callers don't need to know how many bytes are available.

Don't return number of available bytes.  Instead, return 0 on success;
otherwise, negative integers on error.

Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20220609084957.3684698-20-tzungbi@kernel.org