msm: mdss: hdmi: fix potential null deference errors

Fix errors in HDMI and HDCP 2.2 driver code that are
related to potential null pointer deferencing and use of
uninitialized variables.

CRs-Fixed: 1026671
Change-Id: Iecf3d1fe5d5268f043617b3fa920fa97bd05f046
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>