staging: comedi: addi_apci_1564: use comedi_handle_event() for timer

The timer subdevice can generate an interrupt. Currently send_sig() is used
to let the task know when the interrupt occurs. Use the dev->read_subdev
and comedi_handle_events() instead.

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>