iwlwifi: fix typo in 'drivers/net/wireless/iwlwifi/Kconfig'

Based on a patch by Miguel.

Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Cc: Miguel Boton <mboton.lkml@gmail.com>
Cc: "John W. Linville" <linville@tuxdriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>