x86/Kconfig: Fix trivial typo

Fix a typo in the Kconfig help text: adverticed -> advertised.

Signed-off-by: Nikolas Nyby <nikolas@gnu.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: trivial@kernel.org
Cc: tglx@linutronix.de
Cc: x86@kernel.org
Link: https://lkml.kernel.org/r/20180825231054.23813-1-nikolas@gnu.org