ASoC: ak5558: Add MODULE_DEVICE_TABLE

Add missed MODULE_DEVICE_TABLE for the driver can be loaded
automatically at boot.

Fixes: 92088477

 ("ASoC: ak5558: Add support for AK5558 ADC driver")
Cc: <stable@vger.kernel.org>
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1614149872-25510-2-git-send-email-shengjiu.wang@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>