staging: r8188eu: convert rtw_free_drv_sw() to void

staging: r8188eu: convert rtw_free_drv_sw() to void

The function rtw_free_drv_sw() always returns _SUCCESS. None of its
callers use the return value. Convert the return type of that function
from u8 to void. This is part of getting rid of _FAIL / _SUCCESS.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Link: https://lore.kernel.org/r/20221002143544.7974-3-straube.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>