hal: Use cached value of bt encoder format for encoder latency

Fixes device switch from A2dp to speaker taking 10+ seconds.
Communication from audio hal to bt ipc lib results in multiple
socket failures with host as BT is disconnecting. Use cached
encoder format rather than querying again, this will avoid adding
additional latency due to encoder latency checks.

CRs-Fixed: 2028982
Change-Id: I91bd8060660efa0ab163c70112eae59b9a594377