midgard: Fix off-by-one in OP_CHANNEL_COUNT
We allocate 2-bits to store the channel count [1, 4], but the values were not adjusted to fit in [0, 3]. Accordingly, fdot4 with a constant exhibited the same issue as fdot3 prior to the OP_CHANNEL_COUNT quirk was introduced to begin with.
Signed-off-by: Alyssa Rosenzweig alyssa@rosenzweig.io