block: cleanup queue_wc_store

Get rid of the local queue_wc_store variable and handling setting and
clearing the QUEUE_FLAG_WC flag diretly instead the if / else if.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230707094239.107968-2-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>