be less verbose on initstate for unexistent modules.

the module may be unloaded, in this case -NOENT is returned but it
should not present an error message
diff --git a/libkmod/libkmod-module.c b/libkmod/libkmod-module.c
index 96be0cb..dfb694d 100644
--- a/libkmod/libkmod-module.c
+++ b/libkmod/libkmod-module.c
@@ -595,7 +595,7 @@
 				return KMOD_MODULE_BUILTIN;
 		}
 
-		ERR(mod->ctx, "could not open '%s': %s\n",
+		DBG(mod->ctx, "could not open '%s': %s\n",
 			path, strerror(-err));
 		return err;
 	}