ASoC: codecs: wcd938x: make sdw dependency explicit in Kconfig

ASoC: codecs: wcd938x: make sdw dependency explicit in Kconfig

currenlty wcd938x has only soundwire interface and depends on
symbols from wcd938x soundwire module, so make this dependency
explicit in Kconfig

Without this one of the randconfig endup setting
CONFIG_SND_SOC_WCD938X=y
CONFIG_SND_SOC_WCD938X_SDW=m
resulting in some undefined reference to wcd938x_sdw* symbols.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 045442228868 ("ASoC: codecs: wcd938x: add audio routing and Kconfig")
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20210713140417.23693-1-srinivas.kandagatla@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>