staging: comedi: pcmda12: remove {LSB,MSB}_PORT macros

These macros rely on a local variable having a specific name.
Remove them.

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