msm: mdss: Initialize ad_info completion during dt probe only

Previously, the ad_info completion structure was initialized every
time ad_input was called, which reset the completion wait_queue. A
completion structure should only be initialized once, in order to
prevent any corruptions of the wait_queue. Instead, we initialize
the completion during dt probe so that the wait_queue is only
initialized once, and during ad_input, we use a safer INIT_COMPLETION
for resetting complete count.

Change-Id: If1fb7c9a9dec2ad1ec1f07b022bdeabe1af41b22
Signed-off-by: Benet Clark <benetc@codeaurora.org>