staging: r8188eu: make rtw_indicate_sta_disassoc_event() static

The function rtw_indicate_sta_disassoc_event() is only used in
rtw_ap.c. Make it 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/20220819125428.8412-4-straube.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>