dt-bindings: phy: update phy-cadence-sierra.yaml reference

Changeset ba2bf1f0 ("dt-bindings: phy: Add Cadence Sierra PHY bindings in YAML format")
renamed: Documentation/devicetree/bindings/phy/phy-cadence-sierra.txt
to: Documentation/devicetree/bindings/phy/phy-cadence-sierra.yaml.

Update its cross-reference accordingly.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/3550b08d4e8312e7d4a247a3515a93a5f0fd04c5.1610535350.git.mchehab+huawei@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/phy/ti,phy-j721e-wiz.yaml

@@ -151,7 +151,7 @@ patternProperties:
       WIZ node should have '1' subnode for the SERDES. It could be either
       Sierra SERDES or Torrent SERDES. Sierra SERDES should follow the
       bindings specified in
-      Documentation/devicetree/bindings/phy/phy-cadence-sierra.txt
+      Documentation/devicetree/bindings/phy/phy-cadence-sierra.yaml
       Torrent SERDES should follow the bindings specified in
       Documentation/devicetree/bindings/phy/phy-cadence-torrent.yaml