drivers/leds/leds-gpio.c: properly initialize return value

In the event that none of the configs are set (CONFIG_LEDS_GPIO_PLATFORM,
CONFIG_LEDS_GPIO_OF, CONFIG_LEDS_GPIO_PLATFORM), we will return a bogus
value when initializing the module.

Signed-off-by: Davidlohr Bueso <dave@gnu.org>
Acked-by: Richard Purdie <rpurdie@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>