Align the name of operating-points node to dtschema to fix warnings
like:

  opp-table0: $nodename:0: 'opp-table0' does not match '^opp-table(-[a-z0-9]+)?$'
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210819182311.223443-2-krzysztof.kozlowski@canonical.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>