can: kvaser_usb: silence a GCC 12 -Warray-bounds warning

This driver does a lot of casting of smaller buffers to
struct kvaser_cmd_ext, GCC 12 does not like that:

| drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c:489:65: warning: array subscript ‘struct kvaser_cmd_ext[0]’ is partly outside array bounds of ‘unsigned char[32]’ [-Warray-bounds]
| drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c:489:23: note: in expansion of macro ‘le16_to_cpu’
|   489 |                 ret = le16_to_cpu(((struct kvaser_cmd_ext *)cmd)->len);
|       |                       ^~~~~~~~~~~

Temporarily silence this warning (move it to W=1 builds).

Link: https://lore.kernel.org/all/20220520194659.2356903-1-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>
Tested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/kvaser_usb/Makefile

 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_CAN_KVASER_USB) += kvaser_usb.o
 kvaser_usb-y = kvaser_usb_core.o kvaser_usb_leaf.o kvaser_usb_hydra.o
+
+# FIXME: temporarily silence -Warray-bounds on non W=1+ builds
+ifndef KBUILD_EXTRA_WARN
+CFLAGS_kvaser_usb_hydra.o += -Wno-array-bounds
+endif