isp1704_charger: Fix missing check

A segfault happens if there's no board information.

Signed-off-by: Felipe Contreras <[e-mail]>
Acked-by: Heikki Krogerus <[e-mail]>
Signed-off-by: Anton Vorontsov <[e-mail]>

drivers/power/isp1704_charger.c

···
 {
 	struct isp1704_charger_data	*board = isp->dev->platform_data;
 
-	if (board->set_power)
+	if (board && board->set_power)
 		board->set_power(on);
 }