kea: correctly eliminate build host paths from installed file

Only the ${B} part should be trimmed, not what follows
(which is subject to change, depending on where the sources are).

(From OE-Core rev: 1e3fc9b7592956af9bd93e0a077c5b9f3fd9ca2e)

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-connectivity/kea/kea_2.6.1.bb

@@ -69,7 +69,7 @@ do_install:append() {
     sed -i -e 's,@SBINDIR@,${sbindir},g' -e 's,@BASE_BINDIR@,${base_bindir},g' \
            -e 's,@LOCALSTATEDIR@,${localstatedir},g' -e 's,@SYSCONFDIR@,${sysconfdir},g' \
            ${D}${systemd_system_unitdir}/kea-dhcp*service ${D}${sbindir}/keactrl
-    sed -i "s:${B}/../${BPN}-${PV}:@abs_top_builddir_placeholder@:g" ${D}${sbindir}/kea-admin
+    sed -i "s:${B}:@abs_top_builddir_placeholder@:g" ${D}${sbindir}/kea-admin
 }
 
 do_install:append() {