block: clear bio->bi_bdev when putting a bio back in the cache

block: clear bio->bi_bdev when putting a bio back in the cache

BugLink: https://bugs.launchpad.net/bugs/2011425
commit 11eb695feb636fa5211067189cad25ac073e7fe5 upstream.

This isn't strictly needed in terms of correctness, but it does allow
polling to know if the bio has been put already by a different task
and hence avoid polling something that we don't need to.

Cc: stable@vger.kernel.org
Fixes: be4d234d7aeb ("bio: add allocation cache abstraction")
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>