Write random seed directly to /dev/urandom

Don't store it in some variable, as may contain non-ASCII or control
characters (or starts with '-').

init/functions

@@ -96,8 +96,7 @@ reload_random_seed() {
     local seed
     local decoded
     seed=$(qubesdb-read /qubes-random-seed)
-    decoded=$(echo "$seed" | base64 -d)
-    echo "$decoded" > /dev/urandom
+    echo "$seed" | base64 -d > /dev/urandom
     qubesdb-rm /qubes-random-seed
 }