staging: comedi: comedi.h: extra clock and gate sources for amplc_dio200

Add constants to "comedi.h" for the extra clock and gate sources
allowed by the new PCIe cards supported by the "amplc_dio200" driver.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>