led: gpio: Fix possible ZERO_SIZE_PTR pointer dereferencing error.

Since we cannot make sure the 'pdata->num_leds' will always be none
zero here, and then if it equals to zero, the kmemdup() will return
ZERO_SIZE_PTR, which equals to ((void *)16).

So this patch fix this with just doing the zero check before calling
kmemdup().
Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

drivers/leds/leds-gpio-register.c

@@ -28,6 +28,9 @@ struct platform_device *__init gpio_led_register_device(
 	struct platform_device *ret;
 	struct gpio_led_platform_data _pdata = *pdata;
 
+	if (!pdata->num_leds)
+		return ERR_PTR(-EINVAL);
+
 	_pdata.leds = kmemdup(pdata->leds,
 			pdata->num_leds * sizeof(*pdata->leds), GFP_KERNEL);
 	if (!_pdata.leds)