hwc2: Trigger refresh if prepare fails

Prepare cycle can fail on a newly connected display
if insufficient pipes are available at this moment.
Trigger refresh so that the other displays can free
up pipes and a valid content can be attached to
virtual display.

CRs-Fixed: 2419907
Change-Id: I275fe779380414c8d9bda33c34a7738b4f01c34f
1 file changed