dmaengine: at_xdmac: fix for chan conf simplification

When simplificating the channel configuration, the cyclic case has been
forgotten. It leads to use bad configuration causing many bugs.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>