net: phy: broadcom: Use bcm54xx_config_clock_delay() for BCM54612E

bcm54612e_config_init() duplicates what bcm54xx_config_clock_delay()
does with respect to configuring RGMII TX/RX delays appropriately.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>