staging: comedi: drivers: usbduxfast.c: fix for DMA buffers on stack

fix for instances of DMA buffer on stack(being passed to usb_control_msg) for
the USB-DUXfast Board driver.

Signed-off-by: Kumar Amit Mehta <gmate.amit@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>