Remove opaque check in preparing dirty region

Since preserve swap is enabled, we need to clear the color buffer
when the scissor rect is prepared for a new process. This prevents
garbage being present from the previous process in the color buffer.

CRs-Fixed: 465346
Change-Id: I98f2009748244751c4b56af8afbdfeb645c13230
Merge remote-tracking branch 'aokp/jb-mr1' into jb-mr1