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

Replacing it to 'exit(1)' to stick to the similar behaviour in the
same function

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
```