arm64: dts: qcom: qcs615: remove disallowed property in spmi bus node

Remove the unevaluated 'cell-index' property from qcs615-ride.dtb
spmi@c440000 to fix the Devicetree validation error reported by the
kernel test robot.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/r/202412272210.GpGmqcPC-lkp@intel.com/


Fixes: 27554e2b ("arm64: dts: qcom: qcs615: Adds SPMI support")
Signed-off-by: Tingguo Cheng <quic_tingguoc@quicinc.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250117-fix-kernel-test-robot-unexpected-property-issue-v2-1-0b68cf481249@quicinc.com


[bjorn: Fixes commit message wording about LKP]
Signed-off-by: Bjorn Andersson <andersson@kernel.org>