iommu/arm-smmu: Cleanup qsmmuv500_iova_to_phys_hard()

qsmmuv500_iova_to_phys_hard() takes in the IOMMU domain as an
input parameter, but only uses it to derive the SMMU domain.
In preparation for moving this function out to a file where
to_smmu_domain() will not be available, require that the input
argument be an SMMU domain, instead of the IOMMU domain. This
change has no functional impact.

Change-Id: I2ac7efbae70df2378dc382d697dcfe7a676b85f2
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>