dt-bindings: mfd: qcom,spmi-pmic: Drop PWM reg dependency

The PWM node is not a separate device and is expected to be part of parent
SPMI PMIC node, thus it obtains the address space from the parent. One IO
address in "reg" is also not correct description because LPG block maps to
several regions.

Fixes: 3f5117be ("dt-bindings: mfd: convert to yaml Qualcomm SPMI PMIC")
Suggested-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>