staging: rtl8192u: Add null check in rtl8192_usb_initendpoints

There is an allocation for priv->rx_urb[16] has no null check,
which may lead to a null pointer dereference.
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Link: https://lore.kernel.org/r/20201226080258.6576-1-dinghao.liu@zju.edu.cnSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192u/r8192U_core.c

@@ -1608,6 +1608,8 @@ static short rtl8192_usb_initendpoints(struct net_device *dev)
 		void *oldaddr, *newaddr;
 
 		priv->rx_urb[16] = usb_alloc_urb(0, GFP_KERNEL);
+		if (!priv->rx_urb[16])
+			return -ENOMEM;
 		priv->oldaddr = kmalloc(16, GFP_KERNEL);
 		if (!priv->oldaddr)
 			return -ENOMEM;