ASoC: hdac_hdmi: Fix possible NULL pointer dereference

Pointers hdac_hdmi_pcm and hda_device_id can be NULL, so add check for
valid pointer to avoid NULL pointer dereference.

Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty@intel.com>
Signed-off-by: Guneshwor Singh <guneshwor.o.singh@intel.com>
Acked-By: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>