dma-mapping: reliably inform about DMA support for IOMMU

If the DMA IOMMU path is going to be used, the appropriate check should
return that DMA is supported.

Fixes: b5c58b2 ("dma-mapping: direct calls for dma-iommu")
Closes: https://lore.kernel.org/all/181e06ff-35a3-434f-b505-672f430bd1cb@notapiano
Reported-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> #KernelCI
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Author: rleon

kernel/dma/mapping.c

@@ -843,6 +843,9 @@ static int dma_supported(struct device *dev, u64 mask)
 
 	if (WARN_ON(ops && use_dma_iommu(dev)))
 		return false;
+
+	if (use_dma_iommu(dev))
+		return true;
 	/*
 	 * ->dma_supported sets the bypass flag, so we must always call
 	 * into the method here unless the device is truly direct mapped.