platform/chrome: cros_ec_proto: check for missing EC_CMD_HOST_EVENT_GET_WAKE_MASK

As with cros_ec_cmd_xfer_status(), etc., it's not enough to simply check
for the return status of send_command() -- that only covers transport or
other similarly-fatal errors. One must also check the ->result field, to
see whether the command really succeeded. If not, we can't use the data
it returns.

The caller of cros_ec_get_host_event_wake_mask() ignores this, and so
for example, on EC's where the command is not implemented, we're using
junk (or in practice, all zeros) for our wake-mask. We should be using a
non-zero default (currently, it's supposed to be all-1's).

Fix this by checking the ->result field and returning -EPROTO for
errors.

I might label this as fixing commit 29d99b96

 ("cros_ec: Don't signal
wake event for non-wake host events"), except that this fix alone
actually may make things worse, as it now allows for a lot more spurious
wakeups. The patch "platform/chrome: cros_ec_proto: ignore battery/AC
wakeups on old ECs" helps to mitigate this.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>