zd1211rw: 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>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200630070404.8207-1-vulab@iscas.ac.cn

drivers/net/wireless/zydas/zd1211rw/zd_usb.c

@@ -600,9 +600,7 @@ void zd_usb_disable_int(struct zd_usb *usb)
 	dev_dbg_f(zd_usb_dev(usb), "urb %p killed\n", urb);
 	usb_free_urb(urb);
 
-	if (buffer)
-		usb_free_coherent(udev, USB_MAX_EP_INT_BUFFER,
-				  buffer, buffer_dma);
+	usb_free_coherent(udev, USB_MAX_EP_INT_BUFFER, buffer, buffer_dma);
 }
 
 static void handle_rx_packet(struct zd_usb *usb, const u8 *buffer,