isp1704_charger: Fix missing check

A segfault happens if there's no board information.
Signed-off-by: NFelipe Contreras <felipe.contreras@gmail.com>
Acked-by: NHeikki Krogerus <krohei@gmail.com>
Signed-off-by: NAnton Vorontsov <cbouatmailru@gmail.com>

drivers/power/isp1704_charger.c

@@ -79,7 +79,7 @@ static void isp1704_charger_set_power(struct isp1704_charger *isp, bool on)
 {
 	struct isp1704_charger_data	*board = isp->dev->platform_data;
 
-	if (board->set_power)
+	if (board && board->set_power)
 		board->set_power(on);
 }