make W=1 reports defined-but-not-used and kernel-doc formatting issues.

No functionality change.

Fixes: d1ede064 ("ASoC: rt715: add RT715 codec driver")
Cc: Jack Yu <jack.yu@realtek.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200113223625.15995-1-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>