dt-bindings: phy: cadence-sierra: drop assigned-clocks

The meta schema from DT schema already defines assigned-clocks, so there
is no need for device schema to mention it at all. There are also no
benefits of having it here and a board could actually need more of clock
assignments than the schema allows.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/devicetree/bindings/phy/phy-cadence-sierra.yaml

···
       - const: pll0_refclk
       - const: pll1_refclk
 
-  assigned-clocks:
-    minItems: 1
-    maxItems: 2
-
-  assigned-clock-parents:
-    minItems: 1
-    maxItems: 2
-
   cdns,autoconf:
     type: boolean
     description: