package/systemd: fix README hash
Fixes: http://autobuild.buildroot.net/results/487/4878af2ed318925ab530062576f91e7a1af47bd5/
Signed-off-by: Titouan Christophe <titouan.christophe@railnova.eu>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Titouan Christophe