block, bfq: fix uaf for bfqq in bfq_exit_icq_bfqq

In the Linux kernel, the following vulnerability has been resolved:

block, bfq: fix uaf for bfqq in bfq_exit_icq_bfqq

Commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'") will access 'bic->bfqq' in bic_set_bfqq(), however, bfq_exit_icq_bfqq() can free bfqq first, and then call bic_set_bfqq(), which will cause uaf.

Fix the problem by moving bfq_exit_bfqq() behind bic_set_bfqq().