Input: cros_ec_keyb - use cros_ec_cmd_xfer_status helper

Input: cros_ec_keyb - use cros_ec_cmd_xfer_status helper

This patch makes use of cros_ec_cmd_xfer_status() instead of
cros_ec_cmd_xfer(). In this case there is no advantage of doing this
apart from that we want to make cros_ec_cmd_xfer() a private function
for the EC protocol and let people only use the
cros_ec_cmd_xfer_status() to return Linux standard error codes.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Link: https://lore.kernel.org/r/20200414210434.1534982-1-enric.balletbo@collabora.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>