char: vcio: Fail probe if rpi_firmware is not found.

Device Tree is now the only supported config mechanism, therefore
uncomment the block of code that fails the probe if the
firmware node can't be found.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>

drivers/char/broadcom/vcio.c

@@ -126,10 +126,9 @@ static int __init vcio_init(void)
 
 	np = of_find_compatible_node(NULL, NULL,
 				     "raspberrypi,bcm2835-firmware");
-/* Uncomment this when we only boot with Device Tree
 	if (!of_device_is_available(np))
 		return -ENODEV;
-*/
+
 	vcio.fw = rpi_firmware_get(np);
 	if (!vcio.fw)
 		return -ENODEV;