arm64: dts: qcom: msm8996: Fixup smp2p node

The SMEM state property name changes between the integration branch and
mainline, update to use the correct one.

Fixes: 2f45d9fc

 ("arm64: dts: msm8996: Add SMP2P and APCS nodes")
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Sarangdhar Joshi <spjoshi@codeaurora.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>