[media] cx231xx: Remove a bogus check for NULL

As reported by kbuild test robot:
	drivers/media/usb/cx231xx/cx231xx-audio.c:445:16-20: ERROR: dev is NULL but dereferenced.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/cx231xx/cx231xx-audio.c

@@ -439,12 +439,6 @@ static int snd_cx231xx_capture_open(struct snd_pcm_substream *substream)
 	dev_dbg(dev->dev,
 		"opening device and trying to acquire exclusive lock\n");
 
-	if (!dev) {
-		dev_err(dev->dev,
-			"BUG: cx231xx can't find device struct. Can't proceed with open\n");
-		return -ENODEV;
-	}
-
 	if (dev->state & DEV_DISCONNECTED) {
 		dev_err(dev->dev,
 			"Can't open. the device was removed.\n");