net: fec: Fix unbalanced PM runtime calls

When unbinding/removing the driver, we will run into the following warnings:

[  259.655198] fec 400d1000.ethernet: 400d1000.ethernet supply phy not found, using dummy regulator
[  259.665065] fec 400d1000.ethernet: Unbalanced pm_runtime_enable!
[  259.672770] fec 400d1000.ethernet (unnamed net_device) (uninitialized): Invalid MAC address: 00:00:00:00:00:00
[  259.683062] fec 400d1000.ethernet (unnamed net_device) (uninitialized): Using random MAC address: f2:3e:93:b7:29:c1
[  259.696239] libphy: fec_enet_mii_bus: probed

Avoid these warnings by balancing the runtime PM calls during fec_drv_remove().

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