iommu: msm: Use CB index as ASID

ASID conflict between 2 CBs can lead to some odd behavior
of SMMU. Present way of ASID allotment can conflict with
the ASID being used by secure world. Use the CB number
as ASID. That will ensure that we will not use any other
ASID which secure world may think of using it.

Change-Id: I622d5c1aee7dac5913706588ae7ff1c490a2981c
Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>