dt-bindings: dwmac: Remove unexpected item.

Remove the unexpected "snps,dwmac" item in the example.

Fixes: 3b840106 ("dt-bindings: dwmac: Add bindings for new Ingenic SoCs.")

Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>