ALSA: usb-audio: make array static const, makes object smaller

Don't populate array names_to_check on the stack but instead it
static.  Makes the object code smaller by 56 bytes.  Also clean
up checkpatch warning by adding extra const for names_to_check
and pointer s.

Before:
    text    data     bss     dec     hex filename
  103512   34380       0  137892   21aa4 ./sound/usb/mixer.o

After:
    text    data     bss     dec     hex filename
  103264   34572       0  137836   21a6c ./sound/usb/mixer.o

(gcc version 10.2.0)
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210803122839.7143-1-colin.king@canonical.comSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer.c

@@ -1572,9 +1572,9 @@ static size_t append_ctl_name(struct snd_kcontrol *kctl, const char *str)
 static void check_no_speaker_on_headset(struct snd_kcontrol *kctl,
 					struct snd_card *card)
 {
-	const char *names_to_check[] = {
+	static const char * const names_to_check[] = {
 		"Headset", "headset", "Headphone", "headphone", NULL};
-	const char **s;
+	const char * const *s;
 	bool found = false;
 
 	if (strcmp("Speaker", kctl->id.name))