staging: r8188eu: make rtw_reset_securitypriv() static

staging: r8188eu: make rtw_reset_securitypriv() static

The function rtw_reset_securitypriv() is only used in rtw_mlme.c.
Make rtw_reset_securitypriv() and its user
rtw_os_indicate_disconnect() static to get one step closer to
removing os_dep/mlme_linux.c.

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/20220819125428.8412-8-straube.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>