ALSA: usb-audio: endpoint : 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/20200727025208.8739-1-vulab@iscas.ac.cnSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/endpoint.c

@@ -615,7 +615,6 @@ static void release_urbs(struct snd_usb_endpoint *ep, int force)
 	for (i = 0; i < ep->nurbs; i++)
 		release_urb_ctx(&ep->urb[i]);
 
-	if (ep->syncbuf)
 	usb_free_coherent(ep->chip->dev, SYNC_URBS * 4,
 			  ep->syncbuf, ep->sync_dma);