iommu/amd: Remove redundant assignment of err

'err' will be initialized and cleanup the redundant initialization.

Cc: Joerg Roedel <joro@8bytes.org>
Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Link: https://lore.kernel.org/r/1621395447-34738-1-git-send-email-zhangshaokun@hisilicon.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>