net: phy: fixed-phy: Make the error path simpler

When platform_device_register_simple() fails we can return
the error immediately instead of jumping to the 'err_pdev'
label.

This makes the error path a bit simpler.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>