staging: r8723au: remove externs and include needed header file

Remove extern declaration and add include of header file to get same.

Addresses checkpatch.pl:
WARNING: externs should be avoided in .c files
Signed-off-by: Alison Schofield <amsfield22@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723au/core/rtw_ap.c

@@ -21,10 +21,7 @@
 #include <rtl8723a_cmd.h>
 #include <rtl8723a_hal.h>
 #include <asm/unaligned.h>
-
-extern unsigned char WMM_OUI23A[];
-extern unsigned char WPS_OUI23A[];
-extern unsigned char P2P_OUI23A[];
+#include <rtw_mlme_ext.h>
 
 void init_mlme_ap_info23a(struct rtw_adapter *padapter)
 {