obmc-mapper: add dependency on systemd

mapper.c includes systemd/sd-bus.h which requires systemd to be
installed before obmc-mapper is built.  This may have been working via
an indirect dependency previously.  Regardless, an explicit dependency
is appropriate.

Change-Id: Ia0c1816568a526c8e96703d866c7b00a1e1b3fc0
Signed-off-by: Rick Altherr <raltherr@google.com>
diff --git a/meta-phosphor/common/recipes-phosphor/dbus/obmc-mapper.bb b/meta-phosphor/common/recipes-phosphor/dbus/obmc-mapper.bb
index 1e887c4..6f11df6 100644
--- a/meta-phosphor/common/recipes-phosphor/dbus/obmc-mapper.bb
+++ b/meta-phosphor/common/recipes-phosphor/dbus/obmc-mapper.bb
@@ -9,6 +9,8 @@
 inherit obmc-phosphor-systemd
 inherit setuptools
 
+DEPENDS += " systemd"
+
 DBUS_SERVICE_${PN} += "org.openbmc.ObjectMapper"
 RDEPENDS_${PN} += " \
         python-xml \