drv/button_adc: fix button combos

This fixes certain button combos that had the thresholds set too close
to the actual value read by the ADC. On some hubs, this caused incorrect
detection of button presses when multiple buttons were pressed.

Thew new values are calculated from the actual electrical circuit.

Partial revert of 0665a27.

Fixes: pybricks/support#237

lib/pbio/drv/button/button_adc.c

@@ -76,24 +76,24 @@ pbio_error_t pbdrv_button_is_pressed(pbio_button_flags_t *pressed) {
         return err;
     }
 
-    if (value > 3654) {
+    if (value > 3872) {
         // no buttons pressed
-    } else if (value > 3155) {
+    } else if (value > 3394) {
         *pressed |= PBIO_BUTTON_RIGHT_UP; // Bluetooth
-    } else if (value > 2885) {
+    } else if (value > 3009) {
         *pressed |= PBIO_BUTTON_RIGHT;
-    } else if (value > 2645) {
+    } else if (value > 2755) {
         *pressed |= PBIO_BUTTON_RIGHT_UP; // Bluetooth
         *pressed |= PBIO_BUTTON_RIGHT;
-    } else if (value > 2454) {
+    } else if (value > 2538) {
         *pressed |= PBIO_BUTTON_LEFT;
-    } else if (value > 2218) {
+    } else if (value > 2327) {
         *pressed |= PBIO_BUTTON_RIGHT_UP; // Bluetooth
         *pressed |= PBIO_BUTTON_LEFT;
-    } else if (value > 2084) {
+    } else if (value > 2141) {
         *pressed |= PBIO_BUTTON_RIGHT;
         *pressed |= PBIO_BUTTON_LEFT;
-    } else if (value > 1800) {
+    } else if (value > 1969) {
         *pressed |= PBIO_BUTTON_RIGHT_UP; // Bluetooth
         *pressed |= PBIO_BUTTON_RIGHT;
         *pressed |= PBIO_BUTTON_LEFT;