schemas: legacy: refine 'PollRate'

PollRate must be > 0.

Tested: Schema Validator Pass

Change-Id: I0461d72da591ab39f94ea0e265588a48ad5c15d9
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/schemas/legacy.json b/schemas/legacy.json
index f22b271..cf40dbd 100644
--- a/schemas/legacy.json
+++ b/schemas/legacy.json
@@ -1192,7 +1192,8 @@
                 "type": "number"
             },
             "PollRate": {
-                "type": "number"
+                "type": "number",
+                "exclusiveMinimum": 0
             },
             "Type": {
                 "type": "string",