can: gs_usb: gs_usb_receive_bulk_callback(): fix error message

Sinc commit 79a6d1bfe114 ("can: gs_usb: gs_usb_receive_bulk_callback():
unanchor URL on usb_submit_urb() error") a failing resubmit URB will print
an info message.

In the case of a short read where netdev has not yet been assigned,
initialize as NULL to avoid dereferencing an undefined value. Also report
the error value of the failed resubmit.

Fixes: 79a6d1bfe114 ("can: gs_usb: gs_usb_receive_bulk_callback(): unanchor URL on usb_submit_urb() error")
Reported-by: Jakub Kicinski <[e-mail]>
Closes: https://lore.kernel.org/all/[e-mail]/
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Marc Kleine-Budde <[e-mail]>

drivers/net/can/usb/gs_usb.c

···
 {
 	struct gs_usb *parent = urb->context;
 	struct gs_can *dev;
-	struct net_device *netdev;
+	struct net_device *netdev = NULL;
 	int rc;
 	struct net_device_stats *stats;
 	struct gs_host_frame *hf = urb->transfer_buffer;
···
 		}
 	} else if (rc != -ESHUTDOWN && net_ratelimit()) {
 		netdev_info(netdev, "failed to re-submit IN URB: %pe\n",
-			    ERR_PTR(urb->status));
+			    ERR_PTR(rc));
 	}
 }