net: phy: fixed: Drop #ifdef CONFIG_DM_ETH around phy_connect_fixed

In drivers/net/phy/Kconfig, CONFIG_PHY_FIXED already depends on
CONFIG_DM_ETH, so the function prototype definition when
CONFIG_DM_ETH=n does nothing, so it can be dropped. It is also
never reachable, since the whole function is already under #ifdef
CONFIG_PHY_FIXED (which again, as I said, depends on CONFIG_DM_ETH=y).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Message-Id: <20210216224804.3355044-3-olteanv@gmail.com>
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>