staging: rtl8188eu: off by one in rtw_set_802_11_add_wep()

"keyid" is used as an offset into the ->dot11DefKey[] array.  The array
has 4 elements.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>