linux-phytec-ti

dmaengine: pl330: Simplify marking a request as unused

Instead of storing a special instruction in the command buffer to mark a request
as currently unused just set the descriptor field to NULL.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>