C2BufferQueueBlockPoolData: Pass GraphicBuffer to migrate() directly

Originally, we pass the array of GraphicBuffer to migrate(), but the
method only needs the target GraphicBuffer.

This CL changes the signature of migrate() method to pass the target
GraphicBuffer directly.

Bug: 174188958
Test: android.media.cts.MediaCodecPlayerTest#testPlaybackSwitchViews

Change-Id: I85fa89a621e1b8e49d07fa15169e5d11a3c3d44e