dt-bindings: iio: st,lsm6dsx: reference common schema for mount-matrix

Reference iio.yaml schema from dtschema to allow already used
mount-matrix property:

  msm8953-xiaomi-daisy.dtb: imu@6a: Unevaluated properties are not allowed ('mount-matrix' was unexpected)

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230507173923.263741-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>