Change GceFrameBufferConfig::getInstance() to return a const&

Coincides with I08dcfe8da032f03a556454199a2d66d29837571d
on the Android-GCE end.

Change-Id: I7d24a7eadaa3f0a69f8baf34af0cfea24447594f
Reviewed-on: https://swiftshader-review.googlesource.com/3082
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Greg Hartman <ghartman@google.com>
1 file changed