Revert tag desc.json renaming

Signed-off-by: Jeremy Johnson <jeremy.johnson@arm.com>
Change-Id: I3620799a01784865b3de1407e70e02582966f6d1
diff --git a/scripts/schemavalidation/desc.schema.json b/scripts/schemavalidation/desc.schema.json
index 226fc68..d7447b1 100644
--- a/scripts/schemavalidation/desc.schema.json
+++ b/scripts/schemavalidation/desc.schema.json
@@ -75,7 +75,7 @@
                 "type": "string"
             }
         },
-        "tags": {
+        "tag": {
             "description": "list of string tags that can be used for test filtering",
             "type": "array",
             "items": {