staging: comedi: mite: introduce mite_sync_dma()

The struct mite_channel 'dir' member specifies if the dma is input
or output. Wrap the mite_sync_input_dma() and mite_sync_output_dma()
functions with a single mite_sync_dma() so that the drivers don't
have to worry about the sync direction.

The functions that actually sync the input/output dma currently return
-1 if an overflow/underrun is detected otherwise they return 0. If an
overflow/underrun is detected the async->event COMEDI_CB_OVERFLOW is
also set.

The callers never check the return value anyway so just make the
functions return void. The async->event can be checked if necessary
to detect any errors.

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>