wifi: nl80211: don't free NULL coalescing rule

If the parsing fails, we can dereference a NULL pointer here.

Cc: stable@vger.kernel.org
Fixes: be29b99a

 ("cfg80211/nl80211: Add packet coalesce support")
Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240418105220.b328f80406e7.Id75d961050deb05b3e4e354e024866f350c68103@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>