dt-bindings: soc: bcm: use absolute path to other schema

Absolute path to other DT schema is preferred over relative one.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20220726115841.101249-2-krzysztof.kozlowski@linaro.org

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>