btrfs: fix bio_size_ok() for max_sectors > 0xffff

The data type of max_sectors in queue settings is unsigned int.  But
this value is stored to the local variable whose type is unsigned short
in bio_size_ok().  This can cause unexpected result when max_sectors >
0xffff.

Cc: Chris Mason <chris.mason@fusionio.com>
Cc: linux-btrfs@vger.kernel.org
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/volumes.c

@@ -5394,7 +5394,7 @@ static int bio_size_ok(struct block_device *bdev, struct bio *bio,
 {
 	struct bio_vec *prev;
 	struct request_queue *q = bdev_get_queue(bdev);
-	unsigned short max_sectors = queue_max_sectors(q);
+	unsigned int max_sectors = queue_max_sectors(q);
 	struct bvec_merge_data bvm = {
 		.bi_bdev = bdev,
 		.bi_sector = sector,