staging: greybus: light: check delay_{on|off} before use

Even though we trust leds core that the pointers should be valid, we are
safer to check delay_{on|off} before use.

Also, this avoid a smatch warning:
drivers/staging/greybus/light.c:484 gb_blink_set()
warn: variable dereferenced before check 'delay_on' (see line 476)
Signed-off-by: NRui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/greybus/light.c

@@ -463,6 +463,9 @@ static int gb_blink_set(struct led_classdev *cdev, unsigned long *delay_on,
 	if (channel->releasing)
 		return -ESHUTDOWN;
 
+	if (!delay_on || !delay_off)
+		return -EINVAL;
+
 	mutex_lock(&channel->lock);
 	ret = gb_pm_runtime_get_sync(bundle);
 	if (ret < 0)