util-docker: Fix the gpu-fs docker image.
util-docker: Fix the gpu-fs docker image.

This was broken, it was actually building he gcn-gpu image, not the
gpu-fs image. This patch fixes this error.

Change-Id: I2d8ca0ea6584d059ddb6c9084de2b3075fb59723
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/60532
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5