Revert "powerpc/fsl_pci: simplify fsl_pci_dma_set_mask"

This reverts commit c6e5485e
due to failures such as:

e1000e 2000:01:00.0: Tx DMA map failed
Signed-off-by: Scott Wood <oss@buserror.net>

arch/powerpc/sysdev/fsl_pci.c

@@ -135,7 +135,7 @@ static int fsl_pci_dma_set_mask(struct device *dev, u64 dma_mask)
 	 * mapping that allows addressing any RAM address from across PCI.
 	 */
 	if (dev_is_pci(dev) && dma_mask >= pci64_dma_offset * 2 - 1) {
-		dev->bus_dma_mask = 0;
+		set_dma_ops(dev, &dma_nommu_ops);
 		set_dma_offset(dev, pci64_dma_offset);
 	}
 
@@ -395,6 +395,10 @@ static void setup_pci_atmu(struct pci_controller *hose)
 				out_be32(&pci->piw[win_idx].piwar,  piwar);
 			}
 
+			/*
+			 * install our own dma_set_mask handler to fixup dma_ops
+			 * and dma_offset
+			 */
 			ppc_md.dma_set_mask = fsl_pci_dma_set_mask;
 
 			pr_info("%pOF: Setup 64-bit PCI DMA window\n", hose->dn);