iommu/virtio: Fix typo in a comment

The double `as' in a comment is repeated, thus it should be removed.

Signed-off-by: Xiang wangx <wangxiang@cdjrlc.com>
Link: https://lore.kernel.org/r/20211216083302.18049-1-wangxiang@cdjrlc.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>