msm: mdss: hdmi: use busy wait instead of completion

Use busy wait while waiting for DDC read and write to complete.
Using completion APIs to wait can result in thread to schedule
and waking up the thread back can cause a delay of 30 - 40 ms
or more. HDCP 2.2 authentication protocol uses some strict
timeouts and can be as low as 20 ms. Avoid any possible
scheduling and use busy wait to complete the DDC transactions
within allowed time.

Change-Id: I1c12d594a6e1e671fbaa4d197e375070deedc78d
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>