rust: block: fix use of BLK_MQ_F_SHOULD_MERGE

BLK_MQ_F_SHOULD_MERGE has was removed [1] and is now in effect by default.
So remove the flag from tag sets of Rust block device drivers.

Link: https://lore.kernel.org/r/20241219060214.1928848-1-hch@lst.de

 [1]
Fixes: 9377b95cda73 ("block: remove BLK_MQ_F_SHOULD_MERGE")
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20241220-merge-flag-fix-v1-1-41b7778dac06@kernel.org


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