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.