blk-mq: setup queue ->tag_set before initializing hctx

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

blk-mq: setup queue ->tag_set before initializing hctx

Commit 7b815817aa58 ("blk-mq: add helper for checking if one CPU is mapped to specified hctx")

needs to check queue mapping via tag set in hctx's cpuhp handler.

However, q->tag_set may not be setup yet when the cpuhp handler is

enabled, then kernel oops is triggered.

Fix the issue by setup queue tag_set before initializing hctx.