drm/msm/dp: fix programming of DisplayPort SDP registers

Fix the programming of DisplayPort SDP registers primarily related
to Audio enable sequence. This would fix potential issues caused by
read/append/write operations on SDP registers which might corrupt
the parity/data bytes. This would lead to audio issues since the DP
controller would treat the corrupt SDP information as invalid data.

Change-Id: Ie1145b84a8250417487a9701989794ebe79aceac
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>