ALSA: echoaudio: constify snd_pcm_ops structures

snd_pcm_ops are not supposed to change at runtime. All functions
working with snd_pcm_ops provided by <sound/pcm.h> work with
const snd_pcm_ops. So mark the non-const structs as const.
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/echoaudio/echoaudio.c

@@ -826,7 +826,7 @@ static snd_pcm_uframes_t pcm_pointer(struct snd_pcm_substream *substream)
 
 
 /* pcm *_ops structures */
-static struct snd_pcm_ops analog_playback_ops = {
+static const struct snd_pcm_ops analog_playback_ops = {
 	.open = pcm_analog_out_open,
 	.close = pcm_close,
 	.ioctl = snd_pcm_lib_ioctl,
@@ -837,7 +837,7 @@ static struct snd_pcm_ops analog_playback_ops = {
 	.pointer = pcm_pointer,
 	.page = snd_pcm_sgbuf_ops_page,
 };
-static struct snd_pcm_ops analog_capture_ops = {
+static const struct snd_pcm_ops analog_capture_ops = {
 	.open = pcm_analog_in_open,
 	.close = pcm_close,
 	.ioctl = snd_pcm_lib_ioctl,
@@ -850,7 +850,7 @@ static struct snd_pcm_ops analog_capture_ops = {
 };
 #ifdef ECHOCARD_HAS_DIGITAL_IO
 #ifndef ECHOCARD_HAS_VMIXER
-static struct snd_pcm_ops digital_playback_ops = {
+static const struct snd_pcm_ops digital_playback_ops = {
 	.open = pcm_digital_out_open,
 	.close = pcm_close,
 	.ioctl = snd_pcm_lib_ioctl,
@@ -862,7 +862,7 @@ static struct snd_pcm_ops digital_playback_ops = {
 	.page = snd_pcm_sgbuf_ops_page,
 };
 #endif /* !ECHOCARD_HAS_VMIXER */
-static struct snd_pcm_ops digital_capture_ops = {
+static const struct snd_pcm_ops digital_capture_ops = {
 	.open = pcm_digital_in_open,
 	.close = pcm_close,
 	.ioctl = snd_pcm_lib_ioctl,