boot-lantiq: Fix compilation with GCC 14

This fixes the following compile problem:
```
arv7506pw11.c: In function 'show_boot_progress':
arv7506pw11.c:59:24: error: 'return' with a value, in function returning void [-Wreturn-mismatch]
   59 |                 return 0;
      |                        ^
arv7506pw11.c:56:6: note: declared here
   56 | void show_boot_progress(int arg)
      |      ^~~~~~~~~~~~~~~~~~
arv7506pw11.c:71:16: error: 'return' with a value, in function returning void [-Wreturn-mismatch]
   71 |         return 0;
      |                ^
arv7506pw11.c:56:6: note: declared here
   56 | void show_boot_progress(int arg)
      |      ^~~~~~~~~~~~~~~~~~
```

Link: https://github.com/openwrt/openwrt/pull/18688
Signed-off-by: Hauke Mehrtens <[email protected]>

package/boot/uboot-lantiq/patches/0115-MIPS-add-board-support-for-Arcadyan-ARV7506PW11.patch

@@ -89,7 +89,7 @@
 +void show_boot_progress(int arg)
 +{
 +	if (!do_gpio_init)
-+		return 0;
++		return;
 +
 +	if (arg >= 0) {
 +		/* Success - turn off the red power LED and turn on the green power LED */
@@ -101,7 +101,7 @@
 +		gpio_set_value(GPIO_POWER_RED, 0);
 +	}
 +
-+	return 0;
++	return;
 +}
 +
 +static const struct ltq_eth_port_config eth_port_config[] = {