common: Print nothing in the __weak checkboard()

Do not print confusing "Board: Unknown" during boot.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>

common/board_info.c

@@ -8,7 +8,6 @@
 
 int __weak checkboard(void)
 {
-	printf("Board: Unknown\n");
 	return 0;
 }