kernel: blk-mq: fix null pointer dereference in blk_mq_clear_rq_mapping()

In the Linux kernel, the following vulnerability has been resolved: blk-mq: fix null pointer dereference in blkmqclearrqmapping Our syzkaller report a null pointer dereference, root cause is following: blkmqallocmapandrqs set-tagshctxidx = blkmqallocmapandrqs blkmqallocmapandrqs blkmqallocrqs //...