dt-bindings: power: gpcv2: correct patternProperties

i.MX8MQ has pgc 'power-domain@a', so correct patternProperties

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220923075427.985504-1-peng.fan@oss.nxp.com


Signed-off-by: Rob Herring <robh@kernel.org>