staging: comedi: ni_660x: use cfc_handle_events()

Use the comedi_fc helper function instead of duplicating the code.

In the Kconfig, COMEDI_NI_660X selects COMEDI_FC indirectly by selecting
COMEDI_NI_TIOCMD which selects COMEDI_MITE which 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>