btrfs: add btrfs_trans_handle->fs_info pointer

btrfs_trans_handle->root is documented as for use for confirming
that the root passed in to start the transaction is the same as the
one ending it.  It's used in several places when an fs_info pointer
is needed, so let's just add an fs_info pointer directly.  Eventually,
the root pointer can be removed.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 3a83631c..93ee1c1 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2196,7 +2196,7 @@
 {
 	if (list_empty(&trans->qgroup_ref_list) && !trans->delayed_ref_elem.seq)
 		return;
-	btrfs_err(trans->root->fs_info,
+	btrfs_err(trans->fs_info,
 		"qgroups not uptodate in trans handle %p:  list is%s empty, "
 		"seq is %#x.%x",
 		trans, list_empty(&trans->qgroup_ref_list) ? "" : " not",