ASoC: soc-dai: Note valid values of sysclock direction

Clock direction is marked as 'unsigned int' but only two values are
currently used in practice. Note these down in the documentation.
Signed-off-by: John Watts <contact@jookia.org>
Link: https://msgid.link/r/20240326-dai_mclk_hint-v1-1-653cbd2d78d9@jookia.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/soc-dai.c

@@ -45,7 +45,7 @@ static inline int _soc_dai_ret(struct snd_soc_dai *dai,
  * @dai: DAI
  * @clk_id: DAI specific clock ID
  * @freq: new clock frequency in Hz
- * @dir: new clock direction - input/output.
+ * @dir: new clock direction (SND_SOC_CLOCK_IN or SND_SOC_CLOCK_OUT)
  *
  * Configures the DAI master (MCLK) or system (SYSCLK) clocking.
  */