staging: r8188eu: remove HW_VAR_MLME_DISCONNECT from SetHwReg8188EU()

staging: r8188eu: remove HW_VAR_MLME_DISCONNECT from SetHwReg8188EU()

SetHwReg8188EU() is called with HW_VAR_MLME_DISCONNECT only from
functions in rtw_mlme_ext.c. Move the functionality into a static
function in rtw_mlme_ext.c and remove the HW_VAR_MLME_DISCONNECT case
from SetHwReg8188EU(). This is part of the ongoing effort to get rid
of the unwanted hal layer.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220329202141.7028-3-straube.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>