iommu/io-pgtable-arm: Fix pgtable allocation in selftest

Commit 4b123757 ("iommu/io-pgtable-arm: Make allocations
NUMA-aware") added a NUMA hint to page table allocation, but the pgtable
selftest doesn't provide an SMMU device parameter. Since dev_to_node
doesn't accept a NULL argument, add a special case for selftest.
Signed-off-by: NJean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

drivers/iommu/io-pgtable-arm.c

@@ -237,7 +237,8 @@ static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp,
 	void *pages;
 
 	VM_BUG_ON((gfp & __GFP_HIGHMEM));
-	p = alloc_pages_node(dev_to_node(dev), gfp | __GFP_ZERO, order);
+	p = alloc_pages_node(dev ? dev_to_node(dev) : NUMA_NO_NODE,
+			     gfp | __GFP_ZERO, order);
 	if (!p)
 		return NULL;