staging: comedi: addi_apci_3xxx: remove 'tsk_Current' from private data

The interrupt function should be using comedi_event() to let the user
know data is available from the analog input subdevice.

The analog input subdevice is currently broken and nothing sets
tsk_Current anyway so just remove it.

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>