ASoC: dt-bindings: everest,es8328: Require reg property

ES8328 and ES8388 codecs are I2C or SPI devices, thus they are
addressable on their bus and 'reg' property should be always provided.
Requiring 'reg' is pretty close to redundant, because the I2C and SPI
controller/bus bindings require it already, but the convention is to
mention 'reg' also in the device schemas.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20250304103808.75236-2-krzysztof.kozlowski@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>