linux-postmarketos-exynos4: use tag instead of commit (MR 4270)

I forgot to change this before merging. Commit remains the same, so
package itself shouldn't change. Thus:

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

device/community/linux-postmarketos-exynos4/APKBUILD

@@ -36,8 +36,7 @@ case $pkgver in
 	*.*.*)	_kernver=${pkgver%.0};;
 	*.*)	_kernver=$pkgver;;
 esac
-#_tag="v${pkgver//_/-}-exynos4"
-_tag="742d0579779979e732046f17db28e43c9861cce9"
+_tag="v${pkgver//_/-}-exynos4"
 source="
 	$pkgname-$_tag.tar.bz2::$url/-/archive/$_tag/linux-$_tag.tar.bz2
 	$_config
@@ -80,7 +79,7 @@ package() {
 }
 
 sha512sums="
-2bd3c86191254f3d7753b5492a15bab5005c53954ffb182fcf7dd13395481638d535bc0e983e98535bd301db9eeb724866486d11b66ec3f4cbd464df7b17159c  linux-postmarketos-exynos4-742d0579779979e732046f17db28e43c9861cce9.tar.bz2
+23cdbf3ed735704ec14b5f032afd64b0200413c1d17d2917ffa9c11d6087d63830ddce38a2b3b6e70da55fe85265a0325f01f42092ac8a464c4bc9cdcfb773d7  linux-postmarketos-exynos4-v6.4.2-exynos4.tar.bz2
 b313bfb8deacfa48af10c0d0a3d7fca996ca68af7542471080ca46f53d7562a0893383e5779b611b590e63d76d7eec9c134c620dfe522409d4200a01ac367bcd  config-postmarketos-exynos4.armv7
 aaff0332b90e1f9f62de1128cace934717336e54ab09de46477369fa808302482d97334e43a85ee8597c1bcab64d3484750103559fea2ce8cd51776156bf7591  initramfs.list
 09f1f214a24300696809727a7b04378887c06ca6f40803ca51a12bf2176a360b2eb8632139d6a0722094e05cb2038bdb04018a1e3d33fc2697674552ade03bee  init