Fix integer overflow in libgui_test Surface_test

Integer overflow now causes abort (aosp/589659, aosp/589605), causing libgui_test to
fail one of the compositor tests.
Bug: 72229624
Test: adb shell /data/nativetest/libgui_test/libgui_test \
	--gtest_filter=GetFrameTimestampsTest.CompositorTimingUpdatesBasic
Change-Id: I91c77ba53e5ed74034884c8e144e3c3198458aa5
1 file changed