disp: msm: dp: correct the dp_panel instance used to enable audio

When DP_LINK_STATUS_UPDATED irq_hpd occurs, the mst audio instances
are turned off, irq_hpd handled and audio instances are turned on
again. While turning on, an audio instance different from the ones
turned off is being sent, causing ops mismatches eventually leading
to a NOC error. These changes will correct the pointer to the audio
or the panel instances to match the ones that are turned off.

Change-Id: Idd9c013fd64cd6db06bbec34f5083029e4ab522c
Signed-off-by: Sankeerth Billakanti <sbillaka@codeaurora.org>