staging: comedi: pcl816: remove 'int816_mode' from private data

This member of the private data is not needed.

Refactor the interrupt handler and the (*cancel) function to not use
the 'int816_mode' and remove the setting of this member in the (*do_cmd)
heler function.

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>