decklink: Silence no driver / no SO messages

This g_once() is called everywhere, even in provider. This cause
spurious error when device monitor is used. Just silence or remove
the spurious logs.

sys/decklink/gstdecklink.cpp

@@ -1367,7 +1367,7 @@ init_devices (gpointer data)
 
   iterator = CreateDeckLinkIteratorInstance ();
   if (iterator == NULL) {
-    GST_ERROR ("no driver");
+    GST_DEBUG ("no driver");
     return NULL;
   }
 

sys/decklink/linux/DeckLinkAPIDispatch.cpp

@@ -58,7 +58,10 @@ static void	InitDeckLinkAPI (void)
 	libraryHandle = dlopen(kDeckLinkAPI_Name, RTLD_NOW|RTLD_GLOBAL);
 	if (!libraryHandle)
 	{
-		fprintf(stderr, "%s\n", dlerror());
+                /* As we install this plugin regardless if there is a
+                 * proprietary library present or not, let's stay silent
+                 * to avoid poluting the logs */
+		// fprintf(stderr, "%s\n", dlerror());
 		return;
 	}