libstagefright:Buffer size needs to be set on Native Window

In SoftwareRenderer constructor, setting of buffer size was missing, due to
this buffer size of the previous instance was being used by native window.

CRs-Fixed: 420228
(cherry picked from commit b1a38f329a4f973562241f8b8f80c622b654d919)

Change-Id: I1ec05a6ebe2552132251824523731eaaca4f09bf