debug_uart: Remove duplicated carriage return handling

Since commit b391d743 "debug_uart: output CR along with LF", the
handling in puts() is duplicated, not to mention that it should
output carriage return before line feed.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>