staging: r8188eu: make init_addba_retry_timer() static

The function init_addba_retry_timer() is only used in rtw_sta_mgt.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/20220819125428.8412-3-straube.linux@gmail.com


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