dt-bindings: phy: brcm,brcmstb-usb-phy: Fix error in "compatible" conditional schema

The conditional if/then schema has an error as the "enum" values have
"const" in them. Drop the "const".

Signed-off-by: Rob Herring <[e-mail]>
Fixes: 46b616c1574d ("dt-bindings: phy: brcm, brcmstb-usb-phy: add BCM4908 binding")
Acked-by: Rafał Miłecki <[e-mail]>
Message-ID: <[e-mail]>
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/devicetree/bindings/phy/brcm,brcmstb-usb-phy.yaml

···
         compatible:
           contains:
             enum:
-              - const: brcm,bcm4908-usb-phy
-              - const: brcm,brcmstb-usb-phy
+              - brcm,bcm4908-usb-phy
+              - brcm,brcmstb-usb-phy
     then:
       properties:
         reg: