mac80211: init sched_scan_ies

In case that there is an unsupported band, the ie will be
unallocated and the free will crash.

Cc: stable@vger.kernel.org
Signed-off-by: David Spinadel <david.spinadel@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>