net: stmmac: use a local variable for priv->phylink_config

Use a local variable for priv->phylink_config in stmmac_phy_setup()
which makes the code a bit easier to read, allowing some lines to be
merged.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/E1uASLd-0021QR-Cu@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>