ASoC: hdac_hdmi: remove useless initializations

Cppcheck complains a lot about possible null pointer dereferences but
it's again a case of useless initializations to NULL.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210312182246.5153-9-pierre-louis.bossart@linux.intel.com


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