schemas: legacy: constrain 'CPURequired'

This property is used as an index [1] in the code and cannot be
negative.

Tested: Schema Validator Pass

References:
[1] https://github.com/openbmc/dbus-sensors/blob/408061153b93d3cf1699a019bc76dc5cc2b0c356/src/adc/ADCSensorMain.cpp#L221

Change-Id: I45c6a9a7c234d433db4735943b4336d8409511b6
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/schemas/legacy.json b/schemas/legacy.json
index b35ee7a..597a655 100644
--- a/schemas/legacy.json
+++ b/schemas/legacy.json
@@ -932,7 +932,9 @@
                 "type": "number"
             },
             "CPURequired": {
-                "type": "number"
+                "type": "number",
+                "multipleOf": 1,
+                "minimum": 0
             },
             "ChannelNames": {
                 "items": {