iommu/io-pgtable-arm: Clean up faulty sanity check

Checking for a nonzero dma_pfn_offset was a quick shortcut to validate
whether the DMA == phys assumption could hold at all. Checking for a
non-NULL dma_range_map is not quite equivalent, since a map may be
present to describe a limited DMA window even without an offset, and
thus this check can now yield false positives.

However, it only ever served to short-circuit going all the way through
to __arm_lpae_alloc_pages(), failing the canonical test there, and
having a bit more to clean up. As such, we can simply remove it without
loss of correctness.

Reported-by: Naresh Kamboju <[e-mail]>
Signed-off-by: Robin Murphy <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>

drivers/iommu/io-pgtable-arm.c

···
 	if (cfg->oas > ARM_LPAE_MAX_ADDR_BITS)
 		return NULL;
 
-	if (!selftest_running && cfg->iommu_dev->dma_range_map) {
-		dev_err(cfg->iommu_dev, "Cannot accommodate DMA offset for IOMMU page tables\n");
-		return NULL;
-	}
-
 	data = kmalloc(sizeof(*data), GFP_KERNEL);
 	if (!data)
 		return NULL;