common: command add '\n' for debug msg

Add '\n' for debug msg.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>