zynq: fix nix store permission problems

zynq.nix

@@ -35,14 +35,15 @@ in
 
       buildPhase =
         ''
-        cd ${<artiq-zynq>}
         export USER=hydra
+        pushd ${<artiq-zynq>}
         bash ${<artiq-zynq>}/remote_run.sh -h rpi-4 -o "-F /dev/null -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o LogLevel=ERROR -i /opt/hydra_id_rsa" -d ${artiq-zynq.zc706-simple-jtag}
+        popd
 
         sleep 15
 
         cd examples
-        artiq_run mandelbrot.py
+        artiq_run --device-db ${<artiq-zynq>}/examples/device_db.py ${<artiq-zynq>}/examples/mandelbrot.py
 
         touch $out
         '';