sh: guard cookie consistency across termination in the DMA driver

If all descriptors on a channel are terminated or the channel is released,
update the completed cookie counter to match the last cookie. This prevents
inconsistency warning on resumed DMA operation.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>