iommu/mediatek: Correct the flush_iotlb_all callback

Use the correct tlb_flush_all instead of the original one.

Fixes: 4d689b61

 ("iommu/io-pgtable-arm-v7s: Convert to IOMMU API TLB sync")
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>