Btrfs: cleanup of function where btrfs_extend_item() is called

Argument 'trans' became unnecessary from setup_inline_extent_backref()
that called btrfs_extend_item().

Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>