Fix build of cpu in Dockerfile
Fix build of cpu in Dockerfile

The Dockerfile was pulling from a pre-built cpu client,
but we have the source, and if I'm testing the client, I want to
include my changes in the docker build versus pulling the upstream
pre-build binary.

Signed-off-by: Eric Van Hensbergen <08ae98fb185c92c4e7c3d98ea7df248c1b1ab2b3@arm.com>

u-root/cpu,u-root/cpu,u-root/cpu