blk-mq: don't plug for head insertions in blk_execute_rq_nowait

blk-mq: don't plug for head insertions in blk_execute_rq_nowait

[ Upstream commit 50947d7fe9fa6abe3ddc40769dfb02a51c58edb6 ]

Plugs never insert at head, so don't plug for head insertions.

Fixes: 1c2d2fff6dc0 ("block: wire-up support for passthrough plugging")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230413064057.707578-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>