systemd: add missing host-gperf dependency

Fixes:

  http://autobuild.buildroot.org/results/910/91010b43e63b82e050046b8f10c2c42f31a8a620/

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

package/systemd/systemd.mk

@@ -15,7 +15,8 @@ SYSTEMD_DEPENDENCIES = \
 	libcap \
 	dbus \
 	util-linux \
-	kmod
+	kmod \
+	host-gperf
 
 # Make sure that systemd will always be built after busybox so that we have
 # a consistent init setup between two builds