soundwire: stream: constify sdw_port_config when adding devices

sdw_stream_add_master() and sdw_stream_add_slave() do not modify
contents of passed sdw_port_config, so it can be made const for code
safety and as documentation of expected usage.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20231120174720.239610-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>