powerpc/pseries: unwind dma_get_required_mask_pSeriesLP a bit

Call dma_get_required_mask_pSeriesLP directly instead of dma_iommu_ops
to simply the code a bit.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/pseries/iommu.c

@@ -1278,7 +1278,7 @@ static u64 dma_get_required_mask_pSeriesLP(struct device *dev)
 			return DMA_BIT_MASK(64);
 	}
 
-	return dma_iommu_ops.get_required_mask(dev);
+	return dma_iommu_get_required_mask(dev);
 }
 
 static int iommu_mem_notifier(struct notifier_block *nb, unsigned long action,