contrib/vhost-user-blk: fix 32 bit build and enable

contrib/vhost-user-blk: fix 32 bit build and enable

We were not building the vhost-user-blk server due to 32 bit
compilation problems. The problem was due to format string types so
fix that and then enable the build. Tweak the rule to follow the same
rules as other vhost-user daemons.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220321153037.3622127-12-alex.bennee@linaro.org>
Message-Id: <20220524154056.2896913-2-alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>