dmaengine: xilinx: dpdma: Fix race condition in done IRQ

dmaengine: xilinx: dpdma: Fix race condition in done IRQ

[ Upstream commit 868833fbffbe51c487df4f95d4de9194264a4b30 ]

The active descriptor pointer is accessed from different contexts,
including different interrupt handlers, and its access must be protected
by the channel's lock. This wasn't done in the done IRQ handler. Fix it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20210307040629.29308-3-laurent.pinchart@ideasonboard.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>