ALSA: seq: oss: Constify snd_seq_oss_callback definitions

The snd_seq_oss_callback items are just copied to another struct
as-is, hence they can be declared as const.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-53-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/opl3/opl3_oss.c

@@ -16,7 +16,7 @@ static int snd_opl3_reset_seq_oss(struct snd_seq_oss_arg *arg);
 
 /* operators */
 
-static struct snd_seq_oss_callback oss_callback = {
+static const struct snd_seq_oss_callback oss_callback = {
 	.owner = 	THIS_MODULE,
 	.open =		snd_opl3_open_seq_oss,
 	.close =	snd_opl3_close_seq_oss,

sound/synth/emux/emux_oss.c

@@ -34,7 +34,7 @@ static void fake_event(struct snd_emux *emu, struct snd_emux_port *port,
 		       int ch, int param, int val, int atomic, int hop);
 
 /* operators */
-static struct snd_seq_oss_callback oss_callback = {
+static const struct snd_seq_oss_callback oss_callback = {
 	.owner = THIS_MODULE,
 	.open = snd_emux_open_seq_oss,
 	.close = snd_emux_close_seq_oss,