Standardize command usage messages with cmd_usage()

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/board/siemens/common/fpga.c b/board/siemens/common/fpga.c
index ac0022e..63aa179 100644
--- a/board/siemens/common/fpga.c
+++ b/board/siemens/common/fpga.c
@@ -286,7 +286,7 @@
     return 0;
 
  failure:
-    printf ("Usage:\n%s\n", cmdtp->usage);
+    cmd_usage(cmdtp);
     return 1;
 }