After we removed sw_sync_timeline this arg has not been really used by
anyone, all its users pass the size of struct sync_timeline there.

So simplify this function but not requiring the size anymore.
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>