iommu/io-pgtable-arm-v7s: Add error handle for page table allocation failure

In __arm_v7s_alloc_table function:
iommu call kmem_cache_alloc to allocate page table, this function
allocate memory may fail, when kmem_cache_alloc fails to allocate
table, call virt_to_phys will be abnomal and return unexpected phys
and goto out_free, then call kmem_cache_free to release table will
trigger KE, __get_free_pages and free_pages have similar problem,
so add error handle for page table allocation failure.

Fixes: 29859aeb8a6e ("iommu/io-pgtable-arm-v7s: Abort allocation when table address overflows the PTE")
Signed-off-by: Yunfei Wang <[e-mail]>
Cc: <[e-mail]> # 5.10.*
Acked-by: Robin Murphy <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

drivers/iommu/io-pgtable-arm-v7s.c

···
 			__GFP_ZERO | ARM_V7S_TABLE_GFP_DMA, get_order(size));
 	else if (lvl == 2)
 		table = kmem_cache_zalloc(data->l2_tables, gfp);
+
+	if (!table)
+		return NULL;
+
 	phys = virt_to_phys(table);
 	if (phys != (arm_v7s_iopte)phys) {
 		/* Doesn't fit in PTE */
 		dev_err(dev, "Page table does not fit in PTE: %pa", &phys);
 		goto out_free;
 	}
-	if (table && !cfg->coherent_walk) {
+	if (!cfg->coherent_walk) {
 		dma = dma_map_single(dev, table, size, DMA_TO_DEVICE);
 		if (dma_mapping_error(dev, dma))
 			goto out_free;