Fix override setBufferCount

The logic in setBufferCount was still assuming it needed
to inject the extra buffers, however that injection was
already happening in the min_undequeued query. So it was
increasing buffercount by 2x the extraCount, or concretely
5 buffers when it should have been 4 on >75hz devices

Bug: 168928692
Test: Boot coral, verify 4 buffers instead of 5
Change-Id: I0908228a6791d90544fbf4cb21170931bd31a9db