kirkwood: fix typos on DEBUG_LL_UART_*

We were prompted for which DEBUG_LL_UART implementation we want, fix the
typos such that the build continues.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42332 3c298f89-4303-0410-b956-a3cf2f4a3e73