fix example for cuda numbering

tools/starpu_perfmodel_plot.c

@@ -63,7 +63,7 @@ static void usage(char **argv)
         fprintf(stderr, "   -l                  display all available models\n");
         fprintf(stderr, "   -s <symbol>         specify the symbol\n");
 	fprintf(stderr, "   -i <Fxt files>      input FxT files generated by StarPU\n");
-        fprintf(stderr, "   -a <arch>           specify the architecture (e.g. cpu, cpu:k, cuda, gordon)\n");
+        fprintf(stderr, "   -a <arch>           specify the architecture (e.g. cpu, cpu:k, cuda_k, gordon)\n");
         fprintf(stderr, "\n");
 }