dmaengine: at_xdmac: fix to pass correct device identity to free_irq()

free_irq() expects the same device identity that was passed to
corresponding request_irq(), otherwise the IRQ is not freed.

Fixes: e1f7c9ee ("dmaengine: at_xdmac: creation of the atmel eXtended DMA Controller driver")
Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>