btrfs: Use direct way to determine raid56 write/recover mode

Old code used bbio->raid_map to determine whether in raid56
write/recover operation, because we didn't't have bbio->map_type.

Now we have direct way for this condition, rid of using
the function-relative data, and make the code more readable.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/volumes.c

@@ -6068,7 +6068,8 @@ int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
 	bbio->fs_info = root->fs_info;
 	atomic_set(&bbio->stripes_pending, bbio->num_stripes);
 
-	if (bbio->raid_map) {
+	if ((bbio->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK) &&
+	    ((rw & WRITE) || (mirror_num > 1))) {
 		/* In this case, map_length has been set to the length of
 		   a single stripe; not the whole write */
 		if (rw & WRITE) {