Store the reference prior to erasing the reference.

Problem: In post-submit, hwasan complains about use-after-free
for using references after being erased from the map.

Solution: Store the value prior to erasing the reference from
the map.

Test: atest CtsBluetoothTestCases -- --abi arm64-v8a

Bug: 353347429
Bug: 341353017
Change-Id: Iab739e290806a8068ed88b9997f0815875aefd27