staging: r8188eu: replace WIFI_REASON_CODE enum with native ieee80211_reasoncode

WIFI_REASON_CODE is duplication of enum ieee80211_reasoncode.

Signed-off-by: Ivan Safonov <insafonov@gmail.com>
Link: https://lore.kernel.org/r/20200919212443.264126-1-insafonov@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>