hyperv: NULL dereference on error

We try to call free_netvsc_device(net_device) when "net_device" is NULL.
It leads to an Oops.

Fixes: f90251c8a6d0 ('hyperv: Increase the buffer length for netvsc_channel_cb()')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc.c

@@ -1054,10 +1054,8 @@ int netvsc_device_add(struct hv_device *device, void *additional_info)
 	struct net_device *ndev;
 
 	net_device = alloc_net_device(device);
-	if (!net_device) {
-		ret = -ENOMEM;
-		goto cleanup;
-	}
+	if (!net_device)
+		return -ENOMEM;
 
 	net_device->ring_size = ring_size;