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This reverts commit 3ac8eed6, which did
more than it said on the box, and not only it replaced to_phy_driver
with phydev->drv, but it also removed the "!drv" check, without actually
explaining why that is fine.

That patch in fact breaks suspend/resume on any system which has PHY
devices with no drivers bound.

The stack trace is:

Unable to handle kernel NULL pointer dereference at virtual address 00000000000000e8
pc : mdio_bus_phy_suspend+0xd8/0xec
lr : dpm_run_callback+0x38/0x90
Call trace:
 mdio_bus_phy_suspend+0xd8/0xec
 dpm_run_callback+0x38/0x90
 __device_suspend+0x108/0x3cc
 dpm_suspend+0x140/0x210
 dpm_suspend_start+0x7c/0xa0
 suspend_devices_and_enter+0x13c/0x540
 pm_suspend+0x2a4/0x330

Examples why that assumption is not fine:

- There is an MDIO bus with a PHY device that doesn't have a specific
  PHY driver loaded, because mdiobus_register() automatically creates a
  PHY device for it but there is no specific PHY dr...