since the module API is changing, it's a good time to const-ify the description() and key() return values

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@18552 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_musiconhold.c

@@ -1204,7 +1204,7 @@ int unload_module(void)
 	return -1;
 }
 
-char *description(void)
+const char *description(void)
 {
 	return "Music On Hold Resource";
 }
@@ -1222,7 +1222,7 @@ int usecount(void)
 #endif
 }
 
-char *key()
+const char *key()
 {
 	return ASTERISK_GPL_KEY;
 }