dm thin: support a non power of 2 discard_granularity

Support a non-power-of-2 discard granularity in dm-thin, now that the block
layer supports this(via 8dd2cb7e880d2f77fba53b523c99133ad5054cfd "block:
discard granularity might not be power of 2" and
59771079c18c44e39106f0f30054025acafadb41 "blk: avoid divide-by-zero with zero
discard granularity").

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-thin.c

@@ -2443,15 +2443,8 @@ static void set_discard_limits(struct pool_c *pt, struct queue_limits *limits)
 	if (pt->adjusted_pf.discard_passdown) {
 		data_limits = &bdev_get_queue(pt->data_dev->bdev)->limits;
 		limits->discard_granularity = data_limits->discard_granularity;
-	} else if (block_size_is_power_of_two(pool))
+	} else
 		limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
-	else
-		/*
-		 * Use largest power of 2 that is a factor of sectors_per_block
-		 * but at least DATA_DEV_BLOCK_SIZE_MIN_SECTORS.
-		 */
-		limits->discard_granularity = max(1 << (ffs(pool->sectors_per_block) - 1),
-						  DATA_DEV_BLOCK_SIZE_MIN_SECTORS) << SECTOR_SHIFT;
 }
 
 static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)