net/mpc52xx_phy: Various code cleanups

- don't free bus->irq (obsoleted by ca816d98)
- don't dispose irqs (should be done in of_mdiobus_register())
- use fec-pointer consistently in transfer()
- use resource_size()
- cosmetic fixes

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>