ALSA: usb-audio: Make snd_usb_pcm_delay() static

It's a local function, let's make it static.

Link: https://lore.kernel.org/r/20210601162457.4877-2-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/pcm.c

@@ -29,8 +29,8 @@
 #define SUBSTREAM_FLAG_SYNC_EP_STARTED	1
 
 /* return the estimated delay based on USB frame counters */
-snd_pcm_uframes_t snd_usb_pcm_delay(struct snd_usb_substream *subs,
-				    unsigned int rate)
+static snd_pcm_uframes_t snd_usb_pcm_delay(struct snd_usb_substream *subs,
+					   unsigned int rate)
 {
 	int current_frame_number;
 	int frame_diff;

sound/usb/pcm.h

@@ -2,9 +2,6 @@
 #ifndef __USBAUDIO_PCM_H
 #define __USBAUDIO_PCM_H
 
-snd_pcm_uframes_t snd_usb_pcm_delay(struct snd_usb_substream *subs,
-				    unsigned int rate);
-
 void snd_usb_set_pcm_ops(struct snd_pcm *pcm, int stream);
 int snd_usb_pcm_suspend(struct snd_usb_stream *as);
 int snd_usb_pcm_resume(struct snd_usb_stream *as);