Try to match the initial atrac decode size

This ~~uses a buffer~~ skips samples to align the output the same way the PSP aligns its output.  Causes the audio/atrac/decode test to pass (though it needs to test more things.)

This may improve any game that accidentally relies on the first decode pass writing less data, and should improve how well the number of frames from decode match.  I think there was a game JPCSP recently fixed that we suspected this was the case for?

-[Unknown]