badblocks: Fix a nonsense WARN_ON() which checks whether a u64 variable < 0

[ Upstream commit 7e76336e14de9a2b67af96012ddd46c5676cf340 ]

In _badblocks_check(), there are lines of code like this,
1246         sectors -= len;
[snipped]
1251         WARN_ON(sectors < 0);

The WARN_ON() at line 1257 doesn't make sense because sectors is
unsigned long long type and never to be <0.

Fix it by checking directly checking whether sectors is less than len.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Coly Li <colyli@kernel.org>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20250309160556.42854-1-colyli@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

block/badblocks.c

@@ -1349,14 +1349,15 @@ re_check:
 	len = sectors;
 
 update_sectors:
+	/* This situation should never happen */
+	WARN_ON(sectors < len);
+
 	s += len;
 	sectors -= len;
 
 	if (sectors > 0)
 		goto re_check;
 
-	WARN_ON(sectors < 0);
-
 	if (unacked_badblocks > 0)
 		rv = -1;
 	else if (acked_badblocks > 0)