dt-bindings: net: ethernet: Fix JSON pointer references

dt-bindings: net: ethernet: Fix JSON pointer references

A JSON pointer reference (the part after the "#") must start with a "/".
Conversely, references to the entire document must not have a trailing "/"
and should be just a "#". The existing jsonschema package allows these,
but coming changes make allowed "$ref" URIs stricter and throw errors on
these references.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230418150628.1528480-1-robh@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>