arch/mips: change duplicated word in NUMA help text

Fix wording in NUMA help text.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paulburton@kernel.org>
Cc: linux-mips@vger.kernel.org
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>