ALSA: Add const prefix to proc helper functions

Add appropriate const prefix to char * arguments in proc helper functions.
Also fixed the caller side to be proper const pointers.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/core/info.c b/sound/core/info.c
index 35df614..6eb5393 100644
--- a/sound/core/info.c
+++ b/sound/core/info.c
@@ -108,7 +108,7 @@
  *
  * Returns the size of output string.
  */
-int snd_iprintf(struct snd_info_buffer *buffer, char *fmt,...)
+int snd_iprintf(struct snd_info_buffer *buffer, const char *fmt, ...)
 {
 	va_list args;
 	int len, res;
@@ -727,7 +727,7 @@
  * Returns the updated pointer of the original string so that
  * it can be used for the next call.
  */
-char *snd_info_get_str(char *dest, char *src, int len)
+const char *snd_info_get_str(char *dest, const char *src, int len)
 {
 	int c;