hv/netvsc: Fix NULL dereference at single queue mode fallback

The recent commit 916c5e1 ("hv/netvsc: fix handling of fallback
to single queue mode") tried to fix the fallback behavior to a single
queue mode, but it changed the function to return zero incorrectly,
while the function should return an object pointer.  Eventually this
leads to a NULL dereference at the callers that expect non-NULL
value.

Fix it by returning the proper net_device object.

Fixes: 916c5e1 ("hv/netvsc: fix handling of fallback to single queue mode")
Signed-off-by: Takashi Iwai <[email protected]>
Reviewed-by: Stephen Hemminger <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
(cherry picked from commit b19b463)

Orabug: 28671425

Signed-off-by: Liam Merwick <[email protected]>
Reviewed-by: Darren Kenny <[email protected]>
Reviewed-by: Alejandro Jimenez <[email protected]>
Tested-by: Vijay Balakrishna <[email protected]>

Author: tiwai

drivers/net/hyperv/rndis_filter.c

@@ -1338,7 +1338,7 @@ struct netvsc_device *rndis_filter_device_add(struct hv_device *dev,
 	/* setting up multiple channels failed */
 	net_device->max_chn = 1;
 	net_device->num_chn = 1;
-	return 0;
+	return net_device;
 
 err_dev_remv:
 	rndis_filter_device_remove(dev, net_device);