main/postmarketos-base: fix install_if for subpkgs (MR 1713)

Instead of install_if="$pkgname xorg-server" etc, it should be
install_if="$pkgname=$pkgver-r$pkgrel xorg-server".

Reference: https://wiki.alpinelinux.org/wiki/APKBUILD_Reference#install_if

main/postmarketos-base/APKBUILD

@@ -1,6 +1,6 @@
 pkgname=postmarketos-base
 pkgver=5
-pkgrel=0
+pkgrel=1
 pkgdesc="Meta package for minimal postmarketOS base"
 url="https://postmarketos.org"
 arch="noarch"
@@ -62,7 +62,7 @@ package() {
 }
 
 x11() {
-	install_if="$pkgname xorg-server"
+	install_if="$pkgname=$pkgver-r$pkgrel xorg-server"
 	depends="
 		libinput
 		xf86-input-libinput
@@ -71,7 +71,7 @@ x11() {
 }
 
 elogind() {
-	install_if="$pkgname elogind"
+	install_if="$pkgname=$pkgver-r$pkgrel elogind"
 	install="$subpkgname.post-install"
 	mkdir "$subpkgdir"