firmware-samsung-pxa1908: depend OpenRC service on downstream subpackage (MR 5952)

Otherwise the service will be installed even if the mainline kernel is
selected.

Fixes: f59eac28 ("firmware-samsung-pxa1908: move openrc scripts to subpackage (MR 5688)")

device/testing/firmware-samsung-pxa1908/APKBUILD

 pkgname=firmware-samsung-pxa1908
 pkgver=2
-pkgrel=4
+pkgrel=5
 pkgdesc="Firmware for Samsung PXA1908 devices"
 url="https://postmarketos.org"
 arch="aarch64"
@@ -28,7 +28,7 @@ package() {
 }
 
 downstream() {
-	pkgdesc="Service for enabling WLAN on downstream kernels"
+	pkgdesc="Extra firmware files needed by downstream driver"
 	depends="$pkgname"
 
 	mkdir "$subpkgdir"
@@ -41,7 +41,9 @@ downstream() {
 }
 
 downstream_openrc() {
-	install_if="$pkgname=$pkgver-r$pkgrel openrc"
+	pkgdesc="Service for enabling WLAN on downstream kernels"
+	depends="$pkgname-downstream"
+	install_if="$pkgname-downstream=$pkgver-r$pkgrel openrc"
 	install="$subpkgname.post-install"
 
 	install -Dm755 "$srcdir"/sd8x-wlan.initd "$subpkgdir"/etc/init.d/sd8x-wlan