schemas: legacy: constrain 'Index'

'Index' is an integer and not negative.

Tested: Schema Validator Pass

Change-Id: I5cc1528d312005c0b8d39ebb35445a62f261fa02
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/schemas/legacy.json b/schemas/legacy.json
index aded4d3..3a424a3 100644
--- a/schemas/legacy.json
+++ b/schemas/legacy.json
@@ -1010,7 +1010,9 @@
                 "enum": ["Low"]
             },
             "Index": {
-                "type": "number"
+                "type": "number",
+                "minimum": 0,
+                "multipleOf": 1
             },
             "InScaleFactor": {
                 "type": "number"