can: kvaser_usb: hydra: help gcc-13 to figure out cmd_len

Debian's gcc-13 [1] throws the following error in
kvaser_usb_hydra_cmd_size():

[1] gcc version 13.0.0 20221214 (experimental) [master r13-4693-g512098a3316] (Debian 13-20221214-1)

| drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c:502:65: error:
| array subscript ‘struct kvaser_cmd_ext[0]’ is partly outside array
| bounds of ‘unsigned char[32]’ [-Werror=array-bounds=]
|   502 |                 ret = le16_to_cpu(((struct kvaser_cmd_ext *)cmd)->len);

kvaser_usb_hydra_cmd_size() returns the size of given command. It
depends on the command number (cmd->header.cmd_no). For extended
commands (cmd->header.cmd_no == CMD_EXTENDED) the above shown code is
executed.

Help gcc to recognize that this code path is not taken in all cases,
by calling kvaser_usb_hydra_cmd_size() directly after assigning the
command number.

Fixes: aec5fb22

 ("can: kvaser_usb: Add support for Kvaser USB hydra family")
Cc: Jimmy Assarsson <extja@kvaser.com>
Cc: Anssi Hannula <anssi.hannula@bitwise.fi>
Link: https://lore.kernel.org/all/20221219110104.1073881-1-mkl@pengutronix.de
Tested-by: Jimmy Assarsson <extja@kvaser.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>