ASoC: imx-audio-rpmsg: use module_rpmsg_driver to simplify the code

module_rpmsg_driver() makes the code simpler by eliminating
boilerplate code.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20210602082610.3828408-1-yangyingliang@huawei.com


Signed-off-by: Mark Brown <broonie@kernel.org>