clone.sh: If triggered by Gerrit plugin, use its variables

So that the script works as expected with personal fork repos, etc.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I8fcfa09bac3bb663a534f4493cf8eef39c1b019c
diff --git a/clone.sh b/clone.sh
index c2598c1..fbb5ec2 100755
--- a/clone.sh
+++ b/clone.sh
@@ -60,7 +60,12 @@
 }
 
 # Must projects
-TFM_PROJECT="${CODE_REPO:?}"
+if [ -n "${GERRIT_EVENT_HASH}" ]; then
+    # If triggered by Gerrit, use its variables
+    TFM_PROJECT="https://${GERRIT_HOST}/${GERRIT_PROJECT}"
+else
+    TFM_PROJECT="${CODE_REPO:?}"
+fi
 TFM_REFSPEC="${GERRIT_REFSPEC:?}"
 TFM_NAME="trusted-firmware-m"