dt-bindings: mfd: Use full path to other schemas

When referencing other schema, it is preferred to use an absolute path
(/schemas/....), which allows also an seamless move of particular schema
out of Linux kernel to dtschema.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/20240503072116.12430-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Lee Jones <lee@kernel.org>