loop: Use bdev limit helpers for configuring discard

[ Upstream commit 8d3fd059 ]

Instead of directly looking at the request_queue limits, use the bdev
limits helpers, which is preferable.

Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20241030111900.3981223-1-john.g.garry@oracle.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: f5c84eff ("loop: Add sanity check for read/write_iter")
Signed-off-by: Sasha Levin <sashal@kernel.org>