ALSA: usb-audio: Use snprintf instead of sprintf in build_mixer_unit_ctl

Simplified code by removing redundant assignment of sprintf return value
and improved safety by replacing sprintf with snprintf.

Signed-off-by: Zhu Jun <zhujun2@cmss.chinamobile.com>
Link: https://patch.msgid.link/20241009070944.6937-1-zhujun2@cmss.chinamobile.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Author: Zhu Jun

sound/usb/mixer.c

@@ -2224,7 +2224,8 @@ static void build_mixer_unit_ctl(struct mixer_build *state,
 		len = get_term_name(state->chip, iterm, kctl->id.name,
 				    sizeof(kctl->id.name), 0);
 	if (!len)
-		len = sprintf(kctl->id.name, "Mixer Source %d", in_ch + 1);
+		snprintf(kctl->id.name, sizeof(kctl->id.name), "Mixer Source %d", in_ch + 1);
+
 	append_ctl_name(kctl, " Volume");
 
 	usb_audio_dbg(state->chip, "[%d] MU [%s] ch = %d, val = %d/%d\n",