msm: audio: soc: add null checks for hdmi ops

Add null checks to prevent hdmi ops from being called
if they have not been defined.

CRs-Fixed: 1009284
Change-Id: If772bd86cc9b754fbc900eb47338429e9b841eef
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>