dt-bindings: net: tsnep: Fix typo on generic nvmem property

While working on the nvmem description I figured out this file had the
"nvmem-cell-names" property name misspelled. Fix the typo, as
"nvmem-cells-names" has never existed.

Fixes: 603094b2 ("dt-bindings: net: Add tsnep Ethernet controller")
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221104162147.1288230-1-miquel.raynal@bootlin.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/engleder,tsnep.yaml

@@ -47,7 +47,7 @@ properties:
 
   nvmem-cells: true
 
-  nvmem-cells-names: true
+  nvmem-cell-names: true
 
   phy-connection-type:
     enum: