ALSA: Export snd_pcm_constraint_mask64()

Allow modules to use it, fixing a build failure when the newly added
ADAU1977 driver is built as a module.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Mark Brown <broonie@linaro.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_lib.c

@@ -1242,6 +1242,7 @@ int snd_pcm_hw_constraint_mask64(struct snd_pcm_runtime *runtime, snd_pcm_hw_par
 		return -EINVAL;
 	return 0;
 }
+EXPORT_SYMBOL(snd_pcm_hw_constraint_mask64);
 
 /**
  * snd_pcm_hw_constraint_integer - apply an integer constraint to an interval