V4L/DVB: cx231xx: Avoid an OOPS when card is unknown (card=0)

As reported by: Carlos Americo Domiciano <c_domiciano@yahoo.com.br>:

[  220.033500] cx231xx v4l2 driver loaded.
[  220.033571] cx231xx #0: New device Conexant Corporation Polaris AV Capturb @ 480 Mbps (1554:5010) with 6 interfaces
[  220.033577] cx231xx #0: registering interface 0
[  220.033591] cx231xx #0: registering interface 1
[  220.033654] cx231xx #0: registering interface 6
[  220.033910] cx231xx #0: Identified as Unknown CX231xx video grabber (card=0)
[  220.033946] BUG: unable to handle kernel NULL pointer dereference at (null)
[  220.033955] IP: [<ffffffffa0d3c8bd>] cx231xx_pre_card_setup+0x5d/0xb0 [cx231xx]

Thanks-to: Carlos Americo Domiciano <c_domiciano@yahoo.com.br>
Cc: stable@kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/cx231xx/cx231xx-cards.c

@@ -229,6 +229,7 @@ void cx231xx_pre_card_setup(struct cx231xx *dev)
 		     dev->board.name, dev->model);
 
 	/* set the direction for GPIO pins */
+	if (dev->board.tuner_gpio) {
 		cx231xx_set_gpio_direction(dev, dev->board.tuner_gpio->bit, 1);
 		cx231xx_set_gpio_value(dev, dev->board.tuner_gpio->bit, 1);
 		cx231xx_set_gpio_direction(dev, dev->board.tuner_sif_gpio, 1);
@@ -237,6 +238,7 @@ void cx231xx_pre_card_setup(struct cx231xx *dev)
 
 		/* reset the Tuner */
 		cx231xx_gpio_set(dev, dev->board.tuner_gpio);
+	}
 
 	/* set the mode to Analog mode initially */
 	cx231xx_set_mode(dev, CX231XX_ANALOG_MODE);