linux-postmarketos-stericsson: fix project link and pkgdesc (MR 3354)

We are just building upstream Linux with minor patches and no longer
using the linked GitHub repo, so let's fix this to avoid confusion.

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

device/testing/linux-postmarketos-stericsson/APKBUILD

@@ -6,11 +6,11 @@ _flavor="postmarketos-stericsson"
 _config="config-$_flavor.armv7"
 pkgname=linux-$_flavor
 pkgver=5.19_rc2
-pkgrel=0
-pkgdesc="Mainline kernel fork for ST-Ericsson NovaThor devices"
+pkgrel=1
+pkgdesc="Mainline kernel for ST-Ericsson NovaThor devices"
 arch="armv7"
 _carch="arm"
-url="https://github.com/stericsson-mainline/linux"
+url="https://kernel.org"
 license="GPL-2.0-only"
 options="!strip !check !tracedeps
 	pmb:cross-native