iommu/vt-d: Drop duplicate check in dma_pte_free_pagetable()

The BUG_ON check exists in dma_pte_clear_range(), kill the duplicate
check.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/20211025032307.182974-1-wangkefeng.wang@huawei.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20211217083817.1745419-3-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>