MIPS: Kconfig: fix a few trivial spelling mistakes

There are a few spelling mistakes in the Kconfig, fix these.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>