Fix for #6980

Line 7830 prevented successfull compilation when #define CASE_LIGHT_ENABLE is uncommented

Marlin/Marlin_main.cpp

     // CASE LIGHTS (M355)
     #if HAS_CASE_LIGHT
       SERIAL_PROTOCOLLNPGM("Cap:TOGGLE_LIGHTS:1");
-      bool USEABLE_HARDWARE_PWM(uint8_t pin);
       if (USEABLE_HARDWARE_PWM(CASE_LIGHT_PIN)) {
         SERIAL_PROTOCOLLNPGM("Cap:CASE_LIGHT_BRIGHTNESS:1");
       }