staging: comedi: mite.h: remove PCIMIO_COMPAT

The macro `PCIMIO_COMPAT` is defined, but never used.  Remove it.

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>