net: fec: Fix phy_device lookup for phy_reset_after_clk_enable()

The phy_reset_after_clk_enable() is always called with ndev->phydev,
however that pointer may be NULL even though the PHY device instance
already exists and is sufficient to perform the PHY reset.

This condition happens in fec_open(), where the clock must be enabled
first, then the PHY must be reset, and then the PHY IDs can be read
out of the PHY.

If the PHY still is not bound to the MAC, but there is OF PHY node
and a matching PHY device instance already, use the OF PHY node to
obtain the PHY device instance, and then use that PHY device instance
when triggering the PHY reset.

Fixes: 1b0a83ac ("net: fec: add phy_reset_after_clk_enable() support")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: Richard Leitner <richard.leitner@skidata.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>