dmaengine: ti-dma-crossbar: Fix checking return value of devm_ioremap_resource

devm_ioremap_resource returns ERR_PTR on failure.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>