ASoC: doc: Replace open code with params_set_format()

The example code in dpcm.rst contains an open code calling
snd_mask_set(), and this can be better represented with
params_set_format() instead.  This automatically fixes the sparse
warning about snd_pcm_format_t handling, too.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/sound/soc/dpcm.rst

@@ -254,9 +254,7 @@ configuration.
 	channels->min = channels->max = 2;
 
 	/* set DAI0 to 16 bit */
-	snd_mask_set(&params->masks[SNDRV_PCM_HW_PARAM_FORMAT -
-				    SNDRV_PCM_HW_PARAM_FIRST_MASK],
-				    SNDRV_PCM_FORMAT_S16_LE);
+	params_set_format(params, SNDRV_PCM_FORMAT_S16_LE);
 	return 0;
   }