iwlwifi: mvm: combine regular and sched scan stop functions

The regular and scheduled scan functions are very similar, so they can
be combined into one.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>