can: gs_usb: Don't use stack memory for USB transfers

Fixes: 05ca5270005c can: gs_usb: add ethtool set_phys_id callback to locate physical device

The gs_usb driver is performing USB transfers using buffers allocated on
the stack. This causes the driver to not function with vmapped stacks.
Instead, allocate memory for the transfer buffers.

Signed-off-by: Ethan Zonca <e@ethanzonca.com>
Cc: linux-stable <stable@vger.kernel.org> # >= v4.8
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
