iommu/arm-smmu-v3: Remove unnecessary wrapper function

Simplify the code by removing an unnecessary wrapper function.

This was left behind by commit 2f657add
("iommu/arm-smmu-v3: Specialise CMD_SYNC handling")

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>