soundwire: stream: add missing const to Documentation

Commit 21f4c443 ("soundwire: stream: constify sdw_port_config when
adding devices") added const to sdw_port_config argument, but forgot
documentation.

Fixes: 21f4c443 ("soundwire: stream: constify sdw_port_config when adding devices")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240117160639.1327266-1-krzysztof.kozlowski@linaro.org


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