iommu/iova: Init the struct iova to fix the possible memleak

During ethernet(Marvell octeontx2) set ring buffer test:
ethtool -G eth1 rx <rx ring size> tx <tx ring size>
following kmemleak will happen sometimes:

unreferenced object 0xffff000b85421340 (size 64):
  comm "ethtool", pid 867, jiffies 4295323539 (age 550.500s)
  hex dump (first 64 bytes):
    80 13 42 85 0b 00 ff ff ff ff ff ff ff ff ff ff  ..B.............
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<000000001b204ddf>] kmem_cache_alloc+0x1b0/0x350
    [<00000000d9ef2e50>] alloc_iova+0x3c/0x168
    [<00000000ea30f99d>] alloc_iova_fast+0x7c/0x2d8
    [<00000000b8bb2f1f>] iommu_dma_alloc_iova.isra.0+0x12c/0x138
    [<000000002f1a43b5>] __iommu_dma_map+0x8c/0xf8
    [<00000000ecde7899>] iommu_dma_map_page+0x98/0xf8
    [<0000000082004e59>] otx2_alloc_rbuf+0xf4/0x158
    [<000000002b107f6b>] otx2_rq_aura_pool_init+0x110/0x270
    [<00000000c3d563c7>] otx2_open+0x15c/0x734
    [<00000000a2f5f3a8>] otx2_dev_open+0x3c/0x68
    [<00000000456a98b5>] otx2_set_ringparam+0x1ac/0x1d4
    [<00000000f2fbb819>] dev_ethtool+0xb84/0x2028
    [<0000000069b67c5a>] dev_ioctl+0x248/0x3a0
    [<00000000af38663a>] sock_ioctl+0x280/0x638
    [<000000002582384c>] do_vfs_ioctl+0x8b0/0xa80
    [<000000004e1a2c02>] ksys_ioctl+0x84/0xb8

The reason:
When alloc_iova_mem() without initial with Zero, sometimes fpn_lo will
equal to IOVA_ANCHOR by chance, so when return with -ENOMEM(iova32_full)
from __alloc_and_insert_iova_range(), the new_iova will not be freed in
free_iova_mem().

Fixes: bb68b2fb ("iommu/iova: Add rbtree anchor node")
Signed-off-by: Xiaotao Yin <xiaotao.yin@windriver.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iova.c

@@ -233,7 +233,7 @@ static DEFINE_MUTEX(iova_cache_mutex);
 
 struct iova *alloc_iova_mem(void)
 {
-	return kmem_cache_alloc(iova_cache, GFP_ATOMIC);
+	return kmem_cache_zalloc(iova_cache, GFP_ATOMIC);
 }
 EXPORT_SYMBOL(alloc_iova_mem);