Camera3: Clear Metadata channel references
Camera3: Clear Metadata channel references

- When metadata channel initialization fails
  the channel is destroyed but the reference
  to it is kept. This may cause instability
  in the destructor when we try to stop and
  delete this channel again.

BUG: 11045420
Change-Id: I33fe92fd616a286ff80f5e71831cea2b06550548

maruos/android_device_lge_hammerhead,maruos/android_device_lge_hammerhead,maruos/android_device_lge_hammerhead,maruos/android_device_lge_hammerhead