dt-bindings: mfd: st,stpmic1: Merge patterns for nodes

dt-bindings: mfd: st,stpmic1: Merge patterns for nodes

Properties should be described only once, thus having separate pattern
for children just to specify the $ref to regulator.yaml is not correct.
It also makes impossible to finish it with
additional/unevaluatedProperties:false to restrict allowed properties in
regulator node.

Merge the patterns, so each regulator subnode has regulator.yaml $ref,
additional properties and ends with additionalProperties:false.  This
points to missing regulator-min/max-microvolt in LDO4 node.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230726065633.74924-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Lee Jones <lee@kernel.org>