msm: iommu: Don't read from write-only registers

Don't read from V2Pxx command registers when doing
iova-to-phys operations. These registers are write-only and
reading the value before modifying the VA bits is
unnecessary.

Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>