vc: Initial field in constructor

The 'flags' field was our only field not initialized in our
constructor.  To assure consistent behavior, we initialize it
here.

Test: TreeHugger
Change-Id: I92c94eb5a995b5980d635f2c6d1cb12bf28ef4ca

system/bta/vc/devices.h

@@ -68,6 +68,7 @@ class VolumeControlDevice {
         volume(0),
         change_counter(0),
         mute(false),
+        flags(0),
         connection_id(GATT_INVALID_CONN_ID),
         volume_state_handle(0),
         volume_state_ccc_handle(0),