ALSA: usb-audio: More constifications

Apply const prefix to the remaining places: the static table for the
unit information, the mixer maps, the validator tables, etc.

Just for minor optimization and no functional changes.

Link: https://lore.kernel.org/r/20200105144823.29547-12-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/stream.c b/sound/usb/stream.c
index 11785f9..afd5aa5 100644
--- a/sound/usb/stream.c
+++ b/sound/usb/stream.c
@@ -239,7 +239,7 @@ static int add_chmap(struct snd_pcm *pcm, int stream,
 static struct snd_pcm_chmap_elem *convert_chmap(int channels, unsigned int bits,
 						int protocol)
 {
-	static unsigned int uac1_maps[] = {
+	static const unsigned int uac1_maps[] = {
 		SNDRV_CHMAP_FL,		/* left front */
 		SNDRV_CHMAP_FR,		/* right front */
 		SNDRV_CHMAP_FC,		/* center front */
@@ -254,7 +254,7 @@ static struct snd_pcm_chmap_elem *convert_chmap(int channels, unsigned int bits,
 		SNDRV_CHMAP_TC,		/* top */
 		0 /* terminator */
 	};
-	static unsigned int uac2_maps[] = {
+	static const unsigned int uac2_maps[] = {
 		SNDRV_CHMAP_FL,		/* front left */
 		SNDRV_CHMAP_FR,		/* front right */
 		SNDRV_CHMAP_FC,		/* front center */