ARM: u300: fix ages old copy/paste bug

The UART1 is on the fast AHB bridge, not on the slow bus.

Cc: stable@vger.kernel.org
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>