PICA: Properly emulate 1-stage delay in the combiner buffer

This was discovered and verified by @fincs. The tev combiner buffer
actually lags behind by one stage, meaning stage 1 reads the initial
color, stage 2 reads stage 0's output, and so on.

Fixes character portraits in Fire Emblem: Awakening and world textures
in Zelda: ALBW. Closes #1140.