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: 4da46a06 ("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@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>