staging: rtl8192e: Unlock mutex for one line in rtllib_stop_protocol()

staging: rtl8192e: Unlock mutex for one line in rtllib_stop_protocol()

The following command uses the mutex ieee->wx_mutex:
cancel_delayed_work_sync(&ieee->associate_retry_wq)
Therefore it cannot be canceled with ieee->wx_mutex locked.
rtllib_stop_protocol() is always called with ieee->wx_mutex locked so
according line can be unlocked.

Signed-off-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/ffe60e8f6e29197f331e239ab38154da97c743be.1695582999.git.philipp.g.hortmann@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>