Remove use of mapper call

Replace invocations of mapper call with a call to busctl and mapper
get-service.  This provides equivalent functionality but opens the
door for dropping a systemd patch we have carried for some time.

Change-Id: Iea0cce89341939b49b095d1f5010415578331d4d
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/common/recipes-phosphor/flash/obmc-flash-bios/obmc-flash-init.service b/common/recipes-phosphor/flash/obmc-flash-bios/obmc-flash-init.service
index d9355b3..de196d0 100644
--- a/common/recipes-phosphor/flash/obmc-flash-bios/obmc-flash-init.service
+++ b/common/recipes-phosphor/flash/obmc-flash-bios/obmc-flash-init.service
@@ -5,8 +5,8 @@
 
 [Service]
 Restart=no
-ExecStart=/usr/bin/env mapper call /org/openbmc/control/flash/bios org.openbmc.Flash init
-SyslogIdentifier=mapper
+ExecStart=/bin/sh -c "busctl call `mapper get-service /org/openbmc/control/flash/bios` /org/openbmc/control/flash/bios org.openbmc.Flash init"
+SyslogIdentifier=obmc-flash-init
 
 [Install]
 WantedBy={SYSTEMD_DEFAULT_TARGET}