rtlwifi: rtl8192cu: Free ieee80211_hw if probing fails

In case of an error, no one will use the allocated structure. Call
ieee80211_free_hw, same as in rtl_usb_disconnect.

Signed-off-by: Reto Schneider <code@reto-schneider.ch>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200622132113.14508-4-code@reto-schneider.ch