dmaengine: Use Pointer xt after NULL check.

Removing static analysis error:-
Possible null pointer dereference: xt

Because currently xt is dereferenced before NULL check,
Thus Use it after NULL Check.

Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
Reviewed-by: Vaneet Narang <v.narang@samsung.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>