ARM: dts: qcom: mdm9615: align pinctrl subnodes with dt-schema bindings

Align the MDM9615 DT to the expected subnodes namings in the dt-schema
bindings.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221005-mdm9615-pinctrl-yaml-v3-1-e5e045644971@linaro.org