AVRCP: Fix GetItemAttributesCommand

Usecase:
1) Connect DUT with remote device supporting AVRCP 1.4
2) Connect browsing channel (if not already connected).
3) Send request to retrieve player list and select browsed player.
3) Send get item attribute commands to retrieve attributes of particular uid.

Expected Result:
Item attributes of particular UID are retrieved successfully.

Observation:
Get Item Attribute command does not return any response.

Root cause:
Media id passed as argument to MediaBrowse.subscribe is of children instead of
parent as required by the API

Fix:
Refactor to encapsulate requested ID in the subscribe callback, call the
MediaBrowser.subscribe with the correct id.

Test: connect to carkit and check if DUT responds correctly to GetItemAttribute
Bug: 37265436
Change-Id: Ifd7e17c600c0142cd29514eedf4ff8150f632570
(cherry picked from commit 3cd52581)