BLE_Button: Fix advertising settings

Need to use the object private and persistent _adv_data_builder rather
than a local one in the start_advertising function.

Author: LMESTM

Diff for: BLE_Button/source/main.cpp

@@ -75,13 +75,9 @@ class BatteryDemo : ble::Gap::EventHandler {
             ble::adv_interval_t(ble::millisecond_t(1000))
         );
 
-        uint8_t adv_buffer[ble::LEGACY_ADVERTISING_MAX_SIZE];
-
-        ble::AdvertisingDataBuilder adv_data_builder(adv_buffer);
-
-        adv_data_builder.setFlags();
-        adv_data_builder.setLocalServiceList(mbed::make_Span(&_button_uuid, 1));
-        adv_data_builder.setName(DEVICE_NAME);
+        _adv_data_builder.setFlags();
+        _adv_data_builder.setLocalServiceList(mbed::make_Span(&_button_uuid, 1));
+        _adv_data_builder.setName(DEVICE_NAME);
 
         /* Setup advertising */