lttng-babeltrace: fix static build again

I accidentally removed the static build patch when bumping to v1.4.0,
thinking it was merged upstream as of this version, but it's not the
case (it's merged in master), so let's keep the patch file.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>