Add 3rd encoder to VIA keymap (#11580)

keyboards/keebio/bdn9/keymaps/via/keymap.c

@@ -1,5 +1,11 @@
 #include QMK_KEYBOARD_H
 
+enum encoder_names {
+  _LEFT,
+  _RIGHT,
+  _MIDDLE,
+};
+
 enum layer_names {
   _ZERO,
   _ONE,
@@ -36,17 +42,25 @@ const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
 };
 
 void encoder_update_user(uint8_t index, bool clockwise) {
-    if (index == 0) {
+    if (index == _LEFT) {
         if (clockwise) {
             tap_code(KC_VOLU);
         } else {
             tap_code(KC_VOLD);
         }
-    } else if (index == 1) {
+    }
+    else if (index == _MIDDLE) {
+        if (clockwise) {
+            tap_code(KC_DOWN);
+        } else {
+            tap_code(KC_UP);
+        }
+    }
+    else if (index == _RIGHT) {
         if (clockwise) {
-            tap_code(KC_WH_U);
+            tap_code(KC_PGDN);
         } else {
-            tap_code(KC_WH_D);
+            tap_code(KC_PGUP);
         }
     }
 }