Fix failing test in CompositionTest.

This test seems to be broken due to something that bypassed presubmit
while ATP was down.

Fixing the breakage by verifying the correct blend mode

Test: presubmit passes
Test: libsurfaceflinger_unittest passes locally
Change-Id: I8bfeaf4e5458a2a71468db60731b227c5a41c2b0
1 file changed