arm64: dts: qcom: align Google CROS EC PWM node name with dtschema

dtschema expects PWM node name to be a generic "pwm".  This also matches
Devicetree specification requirements about generic node names.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220214081916.162014-4-krzysztof.kozlowski@canonical.com