fix: allow empty parameter while cloning repos

Fixed a bug to allow not specifying any special parameters while cloning
repos from tf.org

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Change-Id: I632aabc29aca460330e573ab66c7b9c594c76c8a
diff --git a/job/tf-sync-repos/sync.sh b/job/tf-sync-repos/sync.sh
index 4924b75..3987db6 100755
--- a/job/tf-sync-repos/sync.sh
+++ b/job/tf-sync-repos/sync.sh
@@ -62,6 +62,8 @@
 	case $2 in
 		--recurse-submodules)
 			;;
+		"")
+			;;
 		*)
 			echo "ERROR: Unknown parameter passed to clone command. sync.sh failed!"
 			exit 1