staging: rtl8821ae: add static for local symbols in rtl_btc.c

This commit fixes the sparse warning:

    "warning: symbol 'X' was not declared. Should it be static?"

Where the X is one of the following

    rtl_btc_operation

Signed-off-by: Konrad Zapalowicz <bergo.torino@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8821ae/btcoexist/rtl_btc.c

@@ -32,7 +32,7 @@
 #include "rtl_btc.h"
 #include "halbt_precomp.h"
 
-struct rtl_btc_ops rtl_btc_operation ={
+static struct rtl_btc_ops rtl_btc_operation = {
 	.btc_init_variables = rtl_btc_init_variables,
 	.btc_init_hal_vars = rtl_btc_init_hal_vars,
 	.btc_init_hw_config = rtl_btc_init_hw_config,