ARM: dts: msm: Modify SDM845 robotics2.0 platform subtype to 6

As SDM845 robotics2.0 platform are assigned new CDT subtype,
we need to modify dts corresponding to 6.

Change-Id: Id80f7bee6d5622264e124f50d49f757d3a8ba3a9
Signed-off-by: Chaojun Wang <chaojun@codeaurora.org>