can: gs_usb: gs_usb_receive_bulk_callback(): check actual_length before accessing...

can: gs_usb: gs_usb_receive_bulk_callback(): check actual_length before accessing header

The driver expects to receive a struct gs_host_frame in
gs_usb_receive_bulk_callback().

Use struct_group to describe the header of the struct gs_host_frame and
check that we have at least received the header before accessing any
members of it.

To resubmit the URB, do not dereference the pointer chain
"dev->parent->hf_size_rx" but use "parent->hf_size_rx" instead. Since
"urb->context" contains "parent", it is always defined, while "dev" is not
defined if the URB it too short.

Fixes: d08e973a77d1 ("can: gs_usb: Added support for the GS_USB CAN devices")
Link: https://patch.msgid.link/20251114-gs_usb-fix-usb-callbacks-v1-2-a29b42eacada@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>