net:phy:marvell: remove unnecessary code

Compile tested.
remove unnecessary code that matches this coccinelle pattern

	ret = phy_write(x, y , z)
	if (ret < 0)
	       	return ret;
	return 0;

As phy_write returns error code, we dont need to do not need extra check
before returning.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>