ALSA: cs423x: More constification

Apply const prefix to the static mapping table.

Just for minor optimization and no functional changes.

Link: https://lore.kernel.org/r/20200105144823.29547-45-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/cs423x/cs4236_lib.c

@@ -80,7 +80,7 @@
  *
  */
 
-static unsigned char snd_cs4236_ext_map[18] = {
+static const unsigned char snd_cs4236_ext_map[18] = {
 	/* CS4236_LEFT_LINE */		0xff,
 	/* CS4236_RIGHT_LINE */		0xff,
 	/* CS4236_LEFT_MIC */		0xdf,