switch positions should honor playhead count

daisyy-looper/ui.h

@@ -462,7 +462,7 @@ class Ui {
           fx_mode = FX_MODE_GRAIN;
           pot_5.setDisplayMode("Grain Num", 100.0f, POT_DISPLAY_MODE_SWITCH_NUMBERS);
           pot_5.setSwitch();
-          pot_5.switch_positions = 8;
+          pot_5.switch_positions = N_PLAYHEADS-1;
           pot_6.setDisplayMode("Grn. Spread", 100.0f, POT_DISPLAY_MODE_PERCENT);
           pot_7.setDisplayMode("Grain Var.", 100.0f, POT_DISPLAY_MODE_PERCENT);
         });