Fix for VirtualDisplay CTS issues.

Following CTS cases fails without the change
1. testEncodeVirtualDisplay
2. testMultipleVirtualDisplays
3. testSingleVirtualDisplay
4. testPrivatePresentationVirtualDisplay
5. testPrivateVirtualDisplay

Issue happens because displaySurface not being initialized
as its becoming local variable and loosing the context.

Change-Id: I54ce623f611faf7fc5d4d00b0d042f9943b57bbe