Btrfs: Pass fs_info to btrfs_num_copies() instead of mapping_tree

This is required for the device replace procedure in a later step.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index ff5d259..ba2b931 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -387,7 +387,7 @@
 		if (test_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags))
 			break;
 
-		num_copies = btrfs_num_copies(&root->fs_info->mapping_tree,
+		num_copies = btrfs_num_copies(root->fs_info,
 					      eb->start, eb->len);
 		if (num_copies == 1)
 			break;