arm64: dts: qcom: msm8996: align node names with DT schema

New slimbus DT schema expect only SLIMbus bus nodes to be named
"slimbus".  In case of Qualcomm SLIMbus NGD, the bus node is what was
called "ngd".

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220928152027.489543-9-krzysztof.kozlowski@linaro.org