btrfs: scrub: replace max_t()/min_t() with clamp() in scrub_throttle_dev_io()

Replace max_t() followed by min_t() with a single clamp().

As was pointed by David Laight in
https://lore.kernel.org/linux-btrfs/20250906122458.75dfc8f0@pumpkin/
the calculation may overflow u32 when the input value is too large, so
clamp_t() is not used.  In practice the expected values are in range of
megabytes to gigabytes (throughput limit) so the bug would not happen.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: David Sterba <dsterba@suse.com>
[ Use clamp() and add explanation. ]
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/scrub.c

@@ -1369,8 +1369,7 @@ static void scrub_throttle_dev_io(struct scrub_ctx *sctx, struct btrfs_device *d
 	 * Slice is divided into intervals when the IO is submitted, adjust by
 	 * bwlimit and maximum of 64 intervals.
 	 */
-	div = max_t(u32, 1, (u32)(bwlimit / (16 * 1024 * 1024)));
-	div = min_t(u32, 64, div);
+	div = clamp(bwlimit / (16 * 1024 * 1024), 1, 64);
 
 	/* Start new epoch, set deadline */
 	now = ktime_get();