postinst-intercepts/update_font_cache: fix ownership of fontconfig cache

The file ownership of the cache files in /var/cache/fontconfig needs to
be set to root:root otherwise it inherits the user and group id of the
build user.

[YOCTO #7411]

(From OE-Core rev: 0ecccc7e75f2833c4f2599ce46b6fb9a0bc06e22)

Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/fontcache.bbclass

@@ -12,7 +12,7 @@ FONT_EXTRA_RDEPENDS ?= "fontconfig-utils"
 fontcache_common() {
 if [ "x$D" != "x" ] ; then
 	$INTERCEPT_DIR/postinst_intercept update_font_cache ${PKG} mlprefix=${MLPREFIX} bindir=${bindir} \
-		libdir=${libdir} base_libdir=${base_libdir}
+		libdir=${libdir} base_libdir=${base_libdir} localstatedir=${localstatedir}
 else
 	fc-cache
 fi