dmaengine: jz4740: Remove extra check

Remove double check on chan->desc.

Found by Coccinelle.

Signed-off-by: Tapasweni Pathak <tapaswenipathak@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>