Fix empty return value in orangepi_set_gpio_mode in wiringPi.c

Call 'return' without an actual value in a function with return value,
while allowed in older GCC, is not allowed and strictly forbidden when
using newer GCC

This fixes the following error when compiling wiringPi with GCC 14:

```
wiringPi.c:7212:49: error: ‘return’ with no value, in function returning non-void [-Wreturn-mismatch]
 7212 |                                                 return;
      |                                                 ^~~~~~
wiringPi.c:6362:5: note: declared here
 6362 | int orangepi_set_gpio_mode(int pin, int mode)
      |     ^~~~~~~~~~~~~~~~~~~~~~
[Compile] mcp23017.c
make: *** [Makefile:85: wiringPi.o] Error 1
```

wiringPi/wiringPi.c

@@ -7209,7 +7209,7 @@ int orangepi_set_gpio_mode(int pin, int mode)
  printf("the pin you choose doesn't support hardware PWM\n");
  printf("OPI:you can select wiringPi pin 33 for PWM pin\n");
  printf("or you can use it in softPwm mode\n");
- return;
+ return 0;
  }
 
  pwm_prd_default = 150000;