usb: appledisplay: remove needless check before usb_free_coherent()

usb_free_coherent() is safe with NULL addr and this check is
not required.

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Link: https://lore.kernel.org/r/20200720052456.7610-1-vulab@iscas.ac.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/appledisplay.c

@@ -305,8 +305,7 @@ error:
 		if (pdata->urb) {
 			usb_kill_urb(pdata->urb);
 			cancel_delayed_work_sync(&pdata->work);
-			if (pdata->urbdata)
-				usb_free_coherent(pdata->udev, ACD_URB_BUFFER_LEN,
+			usb_free_coherent(pdata->udev, ACD_URB_BUFFER_LEN,
 					pdata->urbdata, pdata->urb->transfer_dma);
 			usb_free_urb(pdata->urb);
 		}