main/libisoburn: put back update_config_sub

main/libisoburn/APKBUILD

@@ -16,6 +16,11 @@ makedepends="
 subpackages="$pkgname-dev $pkgname-doc xorriso:_xorriso"
 source="https://files.libburnia-project.org/releases/libisoburn-$pkgver.tar.gz"
 
+prepare() {
+	default_prepare
+	update_config_sub
+}
+
 build() {
 	CFLAGS="$CFLAGS -flto=auto" \
 	./configure \