cfg80211: fix possible memory leak in regdb_query_country()

'wmm_ptrs' is malloced in regdb_query_country() and should be freed
before leaving from the error handling cases, otherwise it will cause
memory leak.

Fixes: 230ebaa1 ("cfg80211: read wmm rules from regulatory database")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
[johannes: add Fixes tag]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>