dmaengine: sprd: Fix the possible memory leak issue

If we terminate the channel to free all descriptors associated with this
channel, we will leak the memory of current descriptor if the current
descriptor is not completed, since it had been deteled from the desc_issued
list and have not been added into the desc_completed list.

Thus we should check if current descriptor is completed or not, when freeing
the descriptors associated with one channel, if not, we should free it to
avoid this issue.

Fixes: 9b3b8171 ("dmaengine: sprd: Add Spreadtrum DMA driver")
Reported-by: Zhenfang Wang <zhenfang.wang@unisoc.com>
Tested-by: Zhenfang Wang <zhenfang.wang@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Link: https://lore.kernel.org/r/170dbbc6d5366b6fa974ce2d366652e23a334251.1570609788.git.baolin.wang@linaro.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>