ALSA: pcm: Fix missing export of snd_pcm_set_sync_per-card()

The recent change for the PCM sync API forgot to export a new API
function that is currently used in emu10k1 driver.

This patch adds the missing export.

Fixes: d712c58c ("ALSA: pcm: optimize and clarify stream synchronization ID API")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202407051343.1Sz8AKFt-lkp@intel.com/Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://patch.msgid.link/20240705063555.17220-1-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_lib.c

@@ -547,6 +547,7 @@ void snd_pcm_set_sync_per_card(struct snd_pcm_substream *substream,
 	strncpy(params->sync + 4, id, len);
 	memset(params->sync + 4 + len, 0, 12 - len);
 }
+EXPORT_SYMBOL_GPL(snd_pcm_set_sync_per_card);
 
 /*
  *  Standard ioctl routine