staging: r8188eu: Fix sparse warning in core/rtw_sta_mgt.c

Sparse reports the following:

  CHECK   drivers/staging/rtl8188eu/core/rtw_sta_mgt.c
drivers/staging/rtl8188eu/core/rtw_sta_mgt.c:152:6: warning: symbol 'rtw_mfree_all_stainfo' was not declared. Should it be static?
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/core/rtw_sta_mgt.c

@@ -149,7 +149,7 @@ inline struct sta_info *rtw_get_stainfo_by_offset(struct sta_priv *stapriv, int
 }
 
 /*  this function is used to free the memory of lock || sema for all stainfos */
-void rtw_mfree_all_stainfo(struct sta_priv *pstapriv)
+static void rtw_mfree_all_stainfo(struct sta_priv *pstapriv)
 {
 	struct list_head *plist, *phead;
 	struct sta_info *psta = NULL;