[media] em28xx-audio: remove needless check before usb_free_coherent()

usb_free_coherent() is safe with NULL addr and this check is
not required.
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/em28xx/em28xx-audio.c

@@ -711,9 +711,7 @@ static void em28xx_audio_free_urb(struct em28xx *dev)
 		if (!urb)
 			continue;
 
-		if (dev->adev.transfer_buffer[i])
-			usb_free_coherent(dev->udev,
-					  urb->transfer_buffer_length,
+		usb_free_coherent(dev->udev, urb->transfer_buffer_length,
 				  dev->adev.transfer_buffer[i],
 				  urb->transfer_dma);