ARM: dts: qcom: mdm9615: drop unit ids from PMIC nodes

On MDM9615 the PMICs are connected using SSBI devices, which do not have
any addressing scheme. Drop the unused unit ids from PMIC device nodes.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220930212052.894834-2-dmitry.baryshkov@linaro.org