ALSA: pcm: remove a superfluous function declaration

Declaration of snd_pcm_drop() in sound/core/pcm_native.c is superfluous
since the function isn't called before being defined. Remove the
declaration.
Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

@@ -1806,8 +1806,6 @@ static const struct action_ops snd_pcm_action_drain_init = {
 	.post_action = snd_pcm_post_drain_init
 };
 
-static int snd_pcm_drop(struct snd_pcm_substream *substream);
-
 /*
  * Drain the stream(s).
  * When the substream is linked, sync until the draining of all playback streams