staging: comedi: pcmda12: remove 'IOSIZE' define

This define has a very generic name. Its only used in one place
so instead of renaming it just remove it and open code the value.

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>