clk: imx7d: correct enet phy ref clock gates

IMX7D_ENET_PHY_REF_ROOT_DIV supplies clock for PHY directly,
there is no clock gate after it, rename it to
IMX7D_ENET_PHY_REF_ROOT_CLK to avoid device tree change.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>