staging: comedi: mite: make mite_ack_linkc() handle mite_sync_dma()

The mite dma is always synced on a LINKC status. Some of the mite users
sync the dma regadless of the status.

Add a 'sync' parameter to mite_ack_linkc() to force a dma sync. Then do
the dma sync as needed.

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>