app_main: Return type to void

Result is not checked

components/esp32/cpu_start.c

@@ -55,7 +55,7 @@ static bool app_cpu_started = false;
 static void do_global_ctors(void);
 static void main_task(void* args);
 extern void ets_setup_syscalls(void);
-extern int app_main(void);
+extern void app_main(void);
 
 extern int _bss_start;
 extern int _bss_end;