staging: r8188eu: convert rtw_free_stainfo() to void

staging: r8188eu: convert rtw_free_stainfo() to void

The function rtw_free_stainfo() returns always _SUCCESS and none of
its callers uses the return value. We can safely make the function
void. Yet another tiny step towards getting rid of _FAIL / _SUCCESS.

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20221101191458.8619-3-straube.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>