btrfs: replace clearing extent buffer dirty bit with btrfs_clean_block

Now that we're passing in the trans into btrfs_clean_tree_block, we can
easily roll in the handling of the !trans case and replace all
occurrences of

	if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags))
		clear_extent_buffer_dirty(eb);

with

	btrfs_tree_lock(eb);
	btrfs_clean_tree_block(eb);
	btrfs_tree_unlock(eb);

We need the lock because if we are actually dirty we need to make sure
we aren't racing with anything that's starting writeout currently.  This
also makes sure that we're accounting fs_info->dirty_metadata_bytes
appropriately.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>