cfg80211: fix rtnl leak in wiphy dump error cases

In two wiphy dump error cases, most often when the dump allocation
must be increased, the RTNL is leaked. This quickly results in a
complete system lockup. Release the RTNL correctly.

Reported-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>