amcc: Clean up command usage output

Update taihu and taishan commands to use cmd_usage() function
to display usage messages.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/board/amcc/taihu/taihu.c b/board/amcc/taihu/taihu.c
index 6e9330f..a98c186 100644
--- a/board/amcc/taihu/taihu.c
+++ b/board/amcc/taihu/taihu.c
@@ -102,13 +102,13 @@
 	int led_no;
 
 	if (argc != 3) {
-		printf("%s", cmd_tp->usage);
+		cmd_usage(cmd_tp);
 		return -1;
 	}
 
 	led_no = simple_strtoul(argv[1], NULL, 16);
 	if (led_no != 1 && led_no != 2) {
-		printf("%s", cmd_tp->usage);
+		cmd_usage(cmd_tp);
 		return -1;
 	}
 
@@ -123,7 +123,7 @@
 		else
 			gpio_write_bit(31, 0);
 	} else {
-		printf("%s", cmd_tp->usage);
+		cmd_usage(cmd_tp);
 		return -1;
 	}