Revert "iommu/amd: Don't allocate with __GFP_ZERO in alloc_coherent"

This reverts commit 5fc872c732.

The DMA-API does not strictly require that the memory
returned by dma_alloc_coherent is zeroed out. For that
another function (dma_zalloc_coherent) should be used. But
all other x86 DMA-API implementation I checked zero out the
memory, so that some drivers rely on it and break when it is
not.

It seems the (driver-)world is not yet ready for this
change, so revert it.

Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/amd_iommu.c

@@ -2930,6 +2930,7 @@ static void *alloc_coherent(struct device *dev, size_t size,
 	size	  = PAGE_ALIGN(size);
 	dma_mask  = dev->coherent_dma_mask;
 	flag     &= ~(__GFP_DMA | __GFP_HIGHMEM | __GFP_DMA32);
+	flag     |= __GFP_ZERO;
 
 	page = alloc_pages(flag | __GFP_NOWARN,  get_order(size));
 	if (!page) {