drm/msm/dp: do not notify audio subsystem if sink doesn't support audio

For sinks that do not support audio, there is no need to notify
audio subsystem of the connection event.

This will make sure that audio routes only to the primary display
when connected to such sinks.

changes in v2:
  - Added fixes tag
  - Removed nested if condition and removed usage of global pointer

Fixes: d13e36d7 ("drm/msm/dp: add audio support for Display Port on MSM")
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>