fix broken download link in the armhf-gnu image

Author: pietroalbini

src/ci/docker/armhf-gnu/Dockerfile

@@ -71,7 +71,8 @@ COPY scripts/qemu-bare-bones-addentropy.c /tmp/addentropy.c
 RUN arm-linux-gnueabihf-gcc addentropy.c -o rootfs/addentropy -static
 
 # TODO: What is this?!
-RUN curl -O http://ftp.nl.debian.org/debian/dists/jessie/main/installer-armhf/current/images/device-tree/vexpress-v2p-ca15-tc1.dtb
+# Source of the file: https://github.com/vfdev-5/qemu-rpi2-vexpress/raw/master/vexpress-v2p-ca15-tc1.dtb
+RUN curl -O https://s3-us-west-1.amazonaws.com/rust-lang-ci2/rust-ci-mirror/vexpress-v2p-ca15-tc1.dtb
 
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh