staging: rtl8821ae: deal with unused functions in halbtc8723b2ant.c

This commit fixes the compiler -Wunused-function warning. It was enough
to put #define around them to supress this warning. One was a special
case because it's usage was commented-out therefore, as I did not want
to remove it completely, I disabled it with #if 0

Conditionally compiled symbols

    halbtc8723b2ant_monitor_bt_enable_disable
    halbtc8723b2ant_set_bt_auto_report
    halbtc8723b2ant_bt_auto_report

Disabled symbols

    halbtc8723b2ant_adc_backoff
    halbtc8723b2ant_set_adc_backoff

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