dmaengine: at_xdmac: Fix race for the tx desc callback

dmaengine: at_xdmac: Fix race for the tx desc callback

The transfer descriptors were wrongly moved to the free descriptors list
before calling the tx desc callback. As the DMA engine drivers drop any
locks before calling the callback function, txd could be taken again,
resulting in its callback called prematurely. Fix the race for the tx desc
callback by moving the xfer desc into the free desc list after the
callback is invoked.

Fixes: e1f7c9eee707 ("dmaengine: at_xdmac: creation of the atmel eXtended DMA Controller driver")
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20211215110115.191749-6-tudor.ambarus@microchip.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>