net: ethernet: lpc_eth: remove unused local variable

A trivial change which removes an unused local variable, the issue
is reported as a compile time warning:

  drivers/net/ethernet/nxp/lpc_eth.c: In function 'lpc_eth_drv_probe':
  drivers/net/ethernet/nxp/lpc_eth.c:1250:21: warning: variable 'phydev' set but not used [-Wunused-but-set-variable]
    struct phy_device *phydev;
                       ^~~~~~

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>