[ALSA] pcm: add snd_pcm_rate_to_rate_bit() helper

Add a snd_pcm_rate_to_rate_bit() function to factor out common code used
by several drivers.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>
diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 2d5dee2..27f8ef4 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -925,6 +925,7 @@
 extern const struct snd_pcm_hw_constraint_list snd_pcm_known_rates;
 
 int snd_pcm_limit_hw_rates(struct snd_pcm_runtime *runtime);
+unsigned int snd_pcm_rate_to_rate_bit(unsigned int rate);
 
 static inline void snd_pcm_set_runtime_buffer(struct snd_pcm_substream *substream,
 					      struct snd_dma_buffer *bufp)