blk-mq: make sure active queue usage is held for bio_integrity_prep()

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

blk-mq: make sure active queue usage is held for bio_integrity_prep()

blk_integrity_unregister() can come if queue usage counter isn't held

for one bio with integrity prepared, so this request may be completed with

calling profile->complete_fn, then kernel panic.

Another constraint is that bio_integrity_prep() needs to be called

before bio merge.

Fix the issue by:

- call bio_integrity_prep() with one queue usage counter grabbed reliably

- call bio_integrity_prep() before bio merge