resources: Update out-of-date title/link

The original link for Hirsute's version of u-boot-qemu was out-dated.
And changed the title from x86 to riscv.

Change-Id: I9f68cb51d6f142d653f66d86cd1cbb3ae5b20178
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-resources/+/62851
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: Jason Lowe-Power <power.jg@gmail.com>
diff --git a/src/riscv-ubuntu/README.md b/src/riscv-ubuntu/README.md
index 6c38d65..58f6802 100644
--- a/src/riscv-ubuntu/README.md
+++ b/src/riscv-ubuntu/README.md
@@ -103,7 +103,7 @@
 download and install the package.
 
 ```sh
-wget http://mirrors.kernel.org/ubuntu/pool/main/u/u-boot/u-boot-qemu_2021.01+dfsg-3ubuntu9_all.deb
+wget http://old-releases.ubuntu.com/ubuntu/pool/main/u/u-boot/u-boot-qemu_2021.01+dfsg-3ubuntu9_all.deb
 dpkg -i u-boot-qemu_2021.01+dfsg-3ubuntu9_all.deb
 apt-get install -f
 ```