Fix functions with empty params (#19647)

* Fix functions with empty params

* Found a bunch more

keyboards/40percentclub/gherkin/keymaps/mjt/keymap.c

@@ -174,13 +174,13 @@ void matrix_init_user(void) {
 
 #ifdef AUDIO_ENABLE
 
-void startup_user()
+void startup_user(void)
 {
     _delay_ms(20); // gets rid of tick
     PLAY_SONG(tone_startup);
 }
 
-void shutdown_user()
+void shutdown_user(void)
 {
     PLAY_SONG(tone_goodbye);
     _delay_ms(150);

keyboards/40percentclub/gherkin/keymaps/steno/keymap.c

@@ -8,6 +8,6 @@ const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
     STN_NUM, STN_NUM, STN_A,   STN_O,   STN_NUM, STN_E,   STN_U,   STN_NUM, STN_NUM, STN_NUM),
 };
 
-void matrix_init_user() {
+void matrix_init_user(void) {
   steno_set_mode(STENO_MODE_GEMINI); // or STENO_MODE_BOLT
 }

keyboards/40percentclub/mf68/keymaps/delivrance/keymap.c

@@ -197,7 +197,7 @@ void led_set_user(uint8_t usb_led) {
 static uint32_t timer;
 static bool is_idle;
 
-void matrix_scan_user() {
+void matrix_scan_user(void) {
     // Check the timer only if the keyboard is not idle
     if (!is_idle) {
         if (timer_elapsed32(timer) >= (uint32_t) BACKLIGHT_IDLE_TIMEOUT * 1000) {

keyboards/40percentclub/ut47/ut47.c

@@ -17,7 +17,7 @@
 #ifdef LED_ENABLE
   #include "uart.h"
 
-void matrix_init_kb() {
+void matrix_init_kb(void) {
   uart_init(9600);
 }
 #endif