plasma-integration: fix cross-build to other wordsize

Turn out KDE_INSTALL_LIBDIR doesn't work.

srcpkgs/plasma-integration/template

@@ -6,7 +6,6 @@ revision=1
 build_style=cmake
 build_helper=qemu
 configure_args="-DBUILD_TESTING=OFF
- -DKDE_INSTALL_LIBDIR=lib
  -DKF6_HOST_TOOLING=/usr/lib/cmake"
 hostmakedepends="extra-cmake-modules pkg-config qt6-base qt6-tools gettext
  qt5-qmake qt5-host-tools qt5-wayland kconfig kcoreaddons wayland-devel
@@ -22,3 +21,8 @@ license="LGPL-2.0-or-later"
 homepage="https://invent.kde.org/plasma/plasma-integration"
 distfiles="${KDE_SITE}/plasma/${version}/${pkgname}-${version}.tar.xz"
 checksum=eef5c21ee43eefa1034126a45d2b34da967af81cf921a9c2a4314a4fb2738913
+
+post_patch() {
+	sed -i '1i set(KDE_INSTALL_QTPLUGINDIR lib/qt6/plugins)' \
+		qt6/CMakeLists.txt
+}