Btrfs: cast bio->bi_sector to a u64 before shifting

On 32 bit machines without CONFIG_LBD, the bi_sector field is only 32 bits.
Btrfs needs to cast it before shifting up, or we end up doing IO into
the wrong place.
Signed-off-by: NChris Mason <chris.mason@oracle.com>

fs/btrfs/inode.c

@@ -386,7 +386,7 @@ int btrfs_merge_bio_hook(struct page *page, unsigned long offset,
 {
 	struct btrfs_root *root = BTRFS_I(page->mapping->host)->root;
 	struct btrfs_mapping_tree *map_tree;
-	u64 logical = bio->bi_sector << 9;
+	u64 logical = (u64)bio->bi_sector << 9;
 	u64 length = 0;
 	u64 map_length;
 	int ret;

fs/btrfs/volumes.c

@@ -2187,7 +2187,7 @@ int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
 	struct btrfs_mapping_tree *map_tree;
 	struct btrfs_device *dev;
 	struct bio *first_bio = bio;
-	u64 logical = bio->bi_sector << 9;
+	u64 logical = (u64)bio->bi_sector << 9;
 	u64 length = 0;
 	u64 map_length;
 	struct btrfs_multi_bio *multi = NULL;