main/postmarketos-ui-mate: fix installation of -openrc subpackage (MR 5627)

[ci:skip-build]: already built successfully in CI

main/postmarketos-ui-mate/APKBUILD

@@ -2,7 +2,7 @@
 # Maintainer: Jakko <jahau@rocketmail.com>
 pkgname=postmarketos-ui-mate
 pkgver=7
-pkgrel=2
+pkgrel=3
 pkgdesc="(X11) MATE Desktop Environment, fork of GNOME2 (stylus recommended)"
 url="http://mate-desktop.org/"
 arch="noarch"
@@ -65,7 +65,7 @@ package() {
 }
 
 openrc() {
-	install="$pkgname=$pkgver-r$pkgrel openrc"
+	install_if="$pkgname=$pkgver-r$pkgrel openrc"
 	install="$subpkgname.post-install $subpkgname.post-upgrade"
 	depends="
 		bluez-openrc