staging: comedi: dt282x: use cfc_handle_events()

Use the comedi_fc helper function to automatically call the subdevice
(*cancel) function when needed and call comedi_event().

This also fixes two bugs.
  1) the analog input command is canceled due to a buffer overflow
     without sending an event (@@ -341,7 +340,7 @@).
  2) an analog output error causes the command to cancel but the event
     is reported to the analog input subdevice (@@ -449,15 +447,13 @@).

In the Kconfig, COMEDI_DT282X already selects COMEDI_FC.

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>