Docker: Update TF-A to use TF-A docker image

Signed-off-by: Benjamin Copeland <ben.copeland@linaro.org>
Change-Id: Iff5ad29726a9e840477ca96f43b2f81aa392654f
diff --git a/tf-a-builder.yaml b/tf-a-builder.yaml
index 2abe389..111474e 100644
--- a/tf-a-builder.yaml
+++ b/tf-a-builder.yaml
@@ -68,7 +68,7 @@
             name: GERRIT_REFSPEC
             default: 'refs/heads/master'
     disabled: false
-    node: docker-amd64-bionic
+    node: docker-amd64-tf-a-bionic
     display-name: 'Trusted Firmware A (TF-A) builder'
     scm:
         - tf-a-ci-scripts