iommu/mediatek: Add list_del in mtk_iommu_remove

iommu/mediatek: Add list_del in mtk_iommu_remove

Lack the list_del in the mtk_iommu_remove, and remove
bus_set_iommu(*, NULL) since there may be several iommu HWs.
we can not bus_set_iommu null when one iommu driver unbind.

This could be a fix for mt2712 which support 2 M4U HW and list them.

Fixes: 7c3a2ec02806 ("iommu/mediatek: Merge 2 M4U HWs into one iommu domain")
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20220503071427.2285-6-yong.wu@mediatek.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>