platform/x86: ideapad-laptop: Add MIIX 720-12IKB to no_hw_rfkill

Yet another Lenovo model to be added to the no_hw_rfkill blacklist:
ideapad MIIX 720-12IKB.  Otherwise it's always hard-blocked.

Reported-by: Robin Roevens <robin.roevens1@pandora.be>
Bugzilla: https://bugzilla.opensuse.org/show_bug.cgi?id=1093035


Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>