Fix fundamental porting errors

FM_CH.setupConnection off-by-one slot index error fix;
FM_SLOT.keyOn volume set fix;
FM_SLOT.set_ar_ksr eg_sh/eg_sel set typo fix;
FM_CH.update_phase_lfo speed-up;
FM_CH.calculate split into FM_SLOT.calculate for readability;
FM_SLOT.calcVol inlined into FM_SLOT.calculate for speed;
OPN.WriteReg now writing to CORRECT slots