When running in software cyclic mode the driver currently does not go back
to the first segment once the last segment has been reached. Effectively
making the transfer non-cyclic.

Fix this by going back to the first segment once the last segment has been
reached for cyclic transfers.

Special care need to be taken to avoid a segment from being submitted
multiple times concurrently, which could happen for transfers with a number
of segments that is smaller than the DMA controller's internal queue.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>