iommu/dma: Fix condition check in iommu_dma_unmap_sg

Clang warns:

drivers/iommu/dma-iommu.c:897:6: warning: logical not is only applied to
the left hand side of this comparison [-Wlogical-not-parentheses]
        if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
            ^                                 ~~
drivers/iommu/dma-iommu.c:897:6: note: add parentheses after the '!' to
evaluate the comparison first
        if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
            ^
             (                                    )
drivers/iommu/dma-iommu.c:897:6: note: add parentheses around left hand
side expression to silence this warning
        if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
            ^
            (                                )
1 warning generated.

Judging from the rest of the commit and the conditional in
iommu_dma_map_sg, either

    if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))

or
    if ((attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)

was intended, not a combination of the two.

I personally think that the former is easier to understand so use that.

Fixes: 06d60728ff ("iommu/dma: move the arm64 wrappers to common code")
Link: https://github.com/ClangBuiltLinux/linux/issues/497
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/dma-iommu.c

@@ -894,7 +894,7 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
 	struct scatterlist *tmp;
 	int i;
 
-	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
+	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
 		iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir);
 
 	/*