leds: Fix ifdef check for gpio_led_register_device()

gpio_led_register_device() is built whenever CONFIG_LEDS_GPIO_REGISTER is
enabled, and this may be used even when CONFIG_NEW_LEDS is turned off.

However, the stub declaration in the header is provided for all configs
without CONFIG_NEW_LEDS, resulting in a build failure:

drivers/leds/leds-gpio-register.c:24:1: error: redefinition of 'gpio_led_register_device'
24 | gpio_led_register_device(int id, const struct gpio_led_platform_data *pdata)
| ^
include/linux/leds.h:646:39: note: previous definition is here

Change the #ifdef check to match the definition.
Note: this apparently took years of randconfig builds to hit, since
a number of other drivers just 'select NEW_LEDS' anyway.

Signed-off-by: Arnd Bergmann <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

include/linux/leds.h

···
 	gpio_blink_set_t	gpio_blink_set;
 };
 
-#ifdef CONFIG_NEW_LEDS
+#ifdef CONFIG_LEDS_GPIO_REGISTER
 struct platform_device *gpio_led_register_device(
 		int id, const struct gpio_led_platform_data *pdata);
 #else