dt-bindings: usb: dwc3: Add Frame Length Adj constraints

In accordance with the IP core databook the
snps,quirk-frame-length-adjustment property can be set within [0, 0x3F].
Let's make sure the DT schema applies a correct constraints on the
property.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20201210090944.16283-15-Sergey.Semin@baikalelectronics.ruSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/snps,dwc3.yaml

@@ -243,6 +243,8 @@ properties:
       length adjustment when the fladj_30mhz_sdbnd signal is invalid or
       incorrect.
     $ref: /schemas/types.yaml#/definitions/uint32
+    minimum: 0
+    maximum: 0x3f
 
   snps,rx-thr-num-pkt-prd:
     description: