wifi: iwlwifi: mvm: fix potential memory leak

wifi: iwlwifi: mvm: fix potential memory leak

If we do get multiple notifications from firmware, then
we might have allocated 'notif', but don't free it. Fix
that by checking for duplicates before allocation.

Fixes: 4da46a06d443 ("wifi: iwlwifi: mvm: Add support for wowlan info notification")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230418122405.116758321cc4.I8bdbcbb38c89ac637eaa20dda58fa9165b25893a@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>