block: fix incorrect branching in blk_max_size_offset()

If non-zero 'chunk_sectors' is passed in to blk_max_size_offset() that
override will be incorrectly ignored.

Old blk_max_size_offset() branching, prior to commit 3ee16db,
must be used only if passed 'chunk_sectors' override is zero.

Fixes: 3ee16db ("dm: fix IO splitting")
Cc: stable@vger.kernel.org # 5.9
Reported-by: John Dorminy <jdorminy@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

include/linux/blkdev.h

@@ -1076,10 +1076,12 @@ static inline unsigned int blk_max_size_offset(struct request_queue *q,
 					       sector_t offset,
 					       unsigned int chunk_sectors)
 {
-	if (!chunk_sectors && q->limits.chunk_sectors)
-		chunk_sectors = q->limits.chunk_sectors;
-	else
-		return q->limits.max_sectors;
+	if (!chunk_sectors) {
+		if (q->limits.chunk_sectors)
+			chunk_sectors = q->limits.chunk_sectors;
+		else
+			return q->limits.max_sectors;
+	}
 
 	if (likely(is_power_of_2(chunk_sectors)))
 		chunk_sectors -= offset & (chunk_sectors - 1);