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/taishan/lcd.c b/board/amcc/taishan/lcd.c
index 624ae40..4e14bbc 100644
--- a/board/amcc/taishan/lcd.c
+++ b/board/amcc/taishan/lcd.c
@@ -167,7 +167,7 @@
 static int do_lcd_puts(cmd_tbl_t * cmdtp, int flag, int argc, char *argv[])
 {
 	if (argc < 2) {
-		printf("%s", cmdtp->usage);
+		cmd_usage(cmdtp);
 		return 1;
 	}
 	lcd_puts(argv[1]);
@@ -176,7 +176,7 @@
 static int do_lcd_putc(cmd_tbl_t * cmdtp, int flag, int argc, char *argv[])
 {
 	if (argc < 2) {
-		printf("%s", cmdtp->usage);
+		cmd_usage(cmdtp);
 		return 1;
 	}
 	lcd_putc((char)argv[1][0]);
@@ -189,7 +189,7 @@
 	char cur_addr;
 
 	if (argc < 3) {
-		printf("%s", cmdtp->usage);
+		cmd_usage(cmdtp);
 		return 1;
 	}