ARM: dts: qcom: SMMU: Remove mmssnoc_axi clock on 8996

The mmssnoc_axi clock is managed by the bus driver so setting a rate on
it can cause conflicts.  Since we have a bus vote in arm-smmu now, just
remove the unnecessary (and dangerous) vote for mmssnoc_axi.

Change-Id: I07f868ab6679aae2af27adc06b7c887538c6a2af
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>