staging: comedi: vmk80xx: include new "comedi_usb.h" header

Include the new "../comedi_usb.h" header instead of <linux/usb.h> and
"../comedidev.h", which will now get included indirectly.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>