x11/xbacklight: Update to 1.2.3

Update x11/xbacklight to 1.2.3
This is a maintenance release

ChangeLog:
https://lists.x.org/archives/xorg-announce/2019-July/003008.html

Obtained from: FreeBSD Graphics Team development repo

		https://github.com/FreeBSDDesktop/freebsd-ports/tree/feature/xorglibs