dt-bindings: can: mpfs: add missing required clock

The CAN controller on PolarFire SoC has an AHB peripheral clock _and_ a
CAN bus clock. The bus clock was omitted when the binding was written,
but is required for operation. Make up for lost time and add it.

Cautionary tale in adding bindings without having implemented a real
user for them perhaps.

Fixes: c878d518d7 ("dt-bindings: can: mpfs: document the mpfs CAN controller")
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

Documentation/devicetree/bindings/net/can/microchip,mpfs-can.yaml

@@ -24,7 +24,9 @@ properties:
     maxItems: 1
 
   clocks:
-    maxItems: 1
+    items:
+      - description: AHB peripheral clock
+      - description: CAN bus clock
 
 required:
   - compatible
@@ -39,7 +41,7 @@ examples:
     can@2010c000 {
         compatible = "microchip,mpfs-can";
         reg = <0x2010c000 0x1000>;
-        clocks = <&clkcfg 17>;
+        clocks = <&clkcfg 17>, <&clkcfg 37>;
         interrupt-parent = <&plic>;
         interrupts = <56>;
     };