msm_fb: HDMI: Cleanup HDMI audio off sequence

HDMI core should not be powered down until the audio engine has
shutdown transmitting packets to the HDMI core. This change
increases the time for which the driver waits for the audio
engine to turn off.

CRs-Fixed: 412575
Change-Id: Ie11ab6c8140f7289f74da4877c9acf9b8cd4a838
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>