get_virtual_functions_linux: would mistakenly always return zero

* src/node_device/node_device_linux_sysfs.c(get_virtual_functions_linux):
Return "ret", rather than always returning 0.

src/node_device/node_device_linux_sysfs.c

@@ -375,7 +375,7 @@ out:
     if (dir)
         closedir(dir);
     VIR_FREE(device_link);
-    return 0;
+    return ret;
 }
 
 #endif /* __linux__ */