hwc: Display view frame needs to be set before using it.

The display view frame needs to be set before calling trimLayer api
because it uses view frame to find the scissor for display, which is
used to clip crop for out-of-bounds display frame sent by framework.
If mViewFrame is not set, scissor will be empty rect, which leads to
wrong source crop calculation.

Change-Id: I52ad4eb9037d34aff24c30fe65e3793684445264