can: gs_usb: gs_usb_receive_bulk_callback(): fix error message

In the Linux kernel, the following vulnerability has been resolved: 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.