staging: comedi: ii_pci20kc: remove CHAN macro

This macro is not used, and it looks to much like the comedi CR_CHAN
macro. Just remove it.

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