net: can: usb: gs_usb: Fix buffer on stack

Allocate buffers on HEAP instead of STACK for local structures
that are to be sent using usb_control_msg().

Signed-off-by: Maksim Salau <maksim.salau@gmail.com>
Cc: linux-stable <stable@vger.kernel.org> # >= v4.8
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>