ALSA: line6: make snd_pcm_ops const

Make these const as they are only passed to a const argument of the
function snd_pcm_set_ops in the file referencing them. Also, add const
to the declaration in the headers.

Structures found using Coccinelle and changes done by hand.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/line6/playback.h b/sound/usb/line6/playback.h
index 51fce29..d8d3b8a 100644
--- a/sound/usb/line6/playback.h
+++ b/sound/usb/line6/playback.h
@@ -27,7 +27,7 @@
  */
 #define USE_CLEAR_BUFFER_WORKAROUND 1
 
-extern struct snd_pcm_ops snd_line6_playback_ops;
+extern const struct snd_pcm_ops snd_line6_playback_ops;
 
 extern int line6_create_audio_out_urbs(struct snd_line6_pcm *line6pcm);
 extern int line6_submit_audio_out_all_urbs(struct snd_line6_pcm *line6pcm);