staging: rtl8723bs: convert function to static

function chk_sta_is_alive() is used only inside core/rtw_ap.c
so remove the prototype and convert it to static.
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Fabio Aiuto <fabioaiuto83@gmail.com>
Link: https://lore.kernel.org/r/20210623130103.7727-1-fabioaiuto83@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/core/rtw_ap.c

@@ -164,8 +164,7 @@ static void update_BCNTIM(struct adapter *padapter)
 	pnetwork_mlmeext->IELength = offset + remainder_ielen;
 }
 
-u8 chk_sta_is_alive(struct sta_info *psta);
-u8 chk_sta_is_alive(struct sta_info *psta)
+static u8 chk_sta_is_alive(struct sta_info *psta)
 {
 	sta_update_last_rx_pkts(psta);