mac80211_hwsim: fix a possible memory leak in hwsim_new_radio_nl()

'hwname' should be freed before leaving from the error handling cases,
otherwise it will cause mem leak

Fixes: cb1a5bae ("mac80211_hwsim: add permanent mac address option for new radios")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>