Codec information missing results in crash.

Problem: Due to race condition, the codec information can be
resetted in the bt_av_co instance. This results in decoder
interface to be initialized to null. When media is streamed,
the null interface results in stack to crash.

Solution: Codec information is retrieved from the decoder update
event instead of the "global" cache. A valid codec config
is retrieved and appropriate decoder is initialized.

Test: m seahawkuserdebug. Tested media use-cases on seahawk.
Bug: 215240360
Tag: #stability
Change-Id: I76b568a5b09e0cd775de0cdd3434fed216f0205f