iwlwifi: remove unnecessary locking

This code, and the places that set the variable
is_internal_short_scan and the vif pointers are
all protected by the mutex, there's no point in
locking the spinlock here as well (any more).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>