clone.sh: fix spm project name and set spm_root

Match the project name used by tf-a-ci-scripts and set the spm_root
environment variable so that the repo cloned based on the topic
can be used by the tf-a-ci-scripts.

Change-Id: I2f51258d1fc27f45b510cf77844d78d9d2950bea
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
diff --git a/tf-a-builder/builders.sh b/tf-a-builder/builders.sh
index d6df203..ff5713f 100755
--- a/tf-a-builder/builders.sh
+++ b/tf-a-builder/builders.sh
@@ -123,6 +123,7 @@
 # Local paths to TF and TFTF repositories
 export tf_root="${tf_root:-${WORKSPACE}/trusted-firmware-a}"
 export tftf_root="${tftf_root:-${WORKSPACE}/tf-a-tests}"
+export spm_root="${spm_root:-${WORKSPACE}/spm}"
 
 # We'd need to see the terminals during development runs, so no need for
 # automation.