wifi: cfg80211: fix memory leak in query_regdb_file()

In the function query_regdb_file() the alpha2 parameter is duplicated
using kmemdup() and subsequently freed in regdb_fw_cb(). However,
request_firmware_nowait() can fail without calling regdb_fw_cb() and
thus leak memory.

Fixes: 007f6c5e ("cfg80211: support loading regulatory database as firmware file")
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>