dt-bindings: clock: mediatek,mtmips-sysc: Adapt compatible for MT7688 boards

As the MT7628 and MT7688 are identical in most respects, mt7628a.dtsi is
used for both SoCs. To prevent "Kernel panic - not syncing: unable to
get CPU clock, err=-2" and allow an MT7688-based board to boot, the
following must be allowed:

compatible = "ralink,mt7628-sysc", "ralink,mt7688-sysc", "syscon";

Signed-off-by: Ezra Buehler <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Acked-by: Sergio Paracuellos <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

Documentation/devicetree/bindings/clock/mediatek,mtmips-sysc.yaml

···
 
 properties:
   compatible:
-    items:
-      - enum:
-          - ralink,mt7620-sysc
-          - ralink,mt7628-sysc
-          - ralink,mt7688-sysc
-          - ralink,rt2880-sysc
-          - ralink,rt3050-sysc
-          - ralink,rt3052-sysc
-          - ralink,rt3352-sysc
-          - ralink,rt3883-sysc
-          - ralink,rt5350-sysc
-      - const: syscon
+    oneOf:
+      - items:
+          - enum:
+              - ralink,mt7620-sysc
+              - ralink,mt7688-sysc
+              - ralink,rt2880-sysc
+              - ralink,rt3050-sysc
+              - ralink,rt3052-sysc
+              - ralink,rt3352-sysc
+              - ralink,rt3883-sysc
+              - ralink,rt5350-sysc
+          - const: syscon
+      - items:
+          - const: ralink,mt7628-sysc
+          - const: ralink,mt7688-sysc
+          - const: syscon
 
   reg:
     maxItems: 1