ASoC: pcm179x: Support continuous rates

According to the PCM179x data sheets sampling frequencies between 10
kHz and 200 kHz are supported. Specify support in the driver.

Tested with PCM1791A.

References:
http://www.ti.com/lit/ds/symlink/pcm1791a.pdf
http://www.ti.com/lit/ds/symlink/pcm1792a.pdf
http://www.ti.com/lit/ds/symlink/pcm1795.pdf
http://www.ti.com/lit/ds/symlink/pcm1796.pdf

Signed-off-by: Jacob Siverskog <[e-mail]>
Reviewed-by: Johan Hovold <[e-mail]>
Acked-by: Michael Trimarchi <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

sound/soc/codecs/pcm179x.c

···
 		.stream_name = "Playback",
 		.channels_min = 2,
 		.channels_max = 2,
-		.rates = PCM1792A_RATES,
+		.rates = SNDRV_PCM_RATE_CONTINUOUS,
+		.rate_min = 10000,
+		.rate_max = 200000,
 		.formats = PCM1792A_FORMATS, },
 	.ops = &pcm179x_dai_ops,
 };

sound/soc/codecs/pcm179x.h

···
 #ifndef __PCM179X_H__
 #define __PCM179X_H__
 
-#define PCM1792A_RATES (SNDRV_PCM_RATE_44100 | SNDRV_PCM_RATE_8000_48000 | \
-			SNDRV_PCM_RATE_88200 | SNDRV_PCM_RATE_96000 | \
-			SNDRV_PCM_RATE_192000)
-
 #define PCM1792A_FORMATS (SNDRV_PCM_FMTBIT_S32_LE | SNDRV_PCM_FMTBIT_S24_LE | \
 			  SNDRV_PCM_FMTBIT_S16_LE)