floss: Refine to use osi_free_and_reset

To simplify codes and guarantee pointers to be set to null.

BUG: 245844505
Tag: #floss
Test: ./build.py
Test: emerge-${BOARD} floss
Test: atest --host net_test_stack_btm
Change-Id: I76b1129232097cb1a7adbc4f58d1e51de90b8d14