MIPS: Netlogic: early console fix

In prom_putchar(), wait for just the TX empty bit to clear in the
UART LSR.

Signed-off-by: Jayachandran C <jayachandranc@netlogicmicro.com>
Cc: linux-mips@linux-mips.org
Cc: Florian Fainelli <florian@openwrt.org>
Patchwork: https://patchwork.linux-mips.org/patch/4112/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>