Add missing parenthesis around error handling code upon attaching

mlx devices. This fixes an issue where mlx device drives fail to be
detected at system boot.

This is a RELENG_6 candidate.

Submitted by:	oliver
PR:		kern/84163

sys/dev/mlx/mlx_pci.c

@@ -212,9 +212,10 @@ mlx_pci_attach(device_t dev)
      * Do bus-independant initialisation.
      */
     error = mlx_attach(sc);
-    if (error != 0)
+    if (error != 0) {
 	mlx_free(sc);
 	return(error);
+    }
     
     /*
      * Start the controller.