useradd.bbclass: use correct value for $D in postinst functions

This corrects the location of the password file used during package installation.

See http://lists.linuxtogo.org/pipermail/openembedded-core/2011-September/009183.html and subsequent discussion.

(From OE-Core rev: 848bb277769af5b094031aeb54d287c158256724)

Signed-off-by: Phil Blundell <philb@gnu.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/useradd.bbclass

@@ -15,8 +15,8 @@ SYSROOT=""
 
 if test "x$D" != "x"; then
 	# Installing into a sysroot
-	SYSROOT="${STAGING_DIR_TARGET}"
-	OPT="--root ${STAGING_DIR_TARGET}"
+	SYSROOT="$D"
+	OPT="--root $D"
 
 	# Add groups and users defined for all recipe packages
 	GROUPADD_PARAM="${@get_all_cmd_params(d, 'group')}"
@@ -79,7 +79,7 @@ useradd_sysroot () {
 
 	# Explicitly set $D since it isn't set to anything
 	# before do_install
-	D=${D}
+	D=${STAGING_DIR_TARGET}
 	useradd_preinst
 }