block: Don't trim an atomic write

This is disallowed.

This check will now be relevant since the device mapper personalities
will start to support atomic writes, and they use this function.

Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
Link: https://lore.kernel.org/r/20250116170301.474130-3-john.g.garry@oracle.com


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