usnic_component.c: don't complain if there are no usNIC devices

cmr=v1.8.2:reviewer=dgoodell

This commit was SVN r31468.

ompi/mca/btl/usnic/btl_usnic_component.c

@@ -514,7 +514,7 @@ static mca_btl_base_module_t** usnic_component_init(int* num_btl_modules,
             opal_output_verbose(5, USNIC_OUT,
                                 "btl:usnic: using L2-only transport");
         } else {
-            mca_btl_base_error_no_nics("usNIC", "device");
+            /* There's no usNICs, so bail... */
             goto free_include_list;
         }
     }