ARM: dts: msm: Use a valid stream-id for sdm845

Use a valid stream-id for the kgsl-iommu test device to prevent error
messages. This issue was introduced by recent upstream changes which
verify that the stream-id is within the allowed range, even though
the test device does not actually need a valid id to operate.

Change-Id: I524439e0f16568387938ce9752d45631441c9aea
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>