msm: vidc: Flush debug message queue before power collpase

Since PC is one of the sync point, flush all the pending FW message
before movig FW to PC state. This helps to avoid the confusion in FW
prints on when PC_PREP command is sent.

CRs-Fixed: 2012520
Change-Id: I94c2117eab764a02103ea0919c46ed9249f192ac
Signed-off-by: Praneeth Paladugu <ppaladug@codeaurora.org>