phylib: fix device deletion order in mdiobus_unregister()

commit 8b63ec18 ("phylib: Make PHYs children of their MDIO bus, not
the bus' parent.") uncovered a problem in mdiobus_unregister() which
leads to this warning when I reboot an APM Mustang (arm64) platform:

  WARNING: CPU: 7 PID: 4239 at fs/sysfs/group.c:224 sysfs_remove_group+0xa0/0xa4()
  sysfs group fffffe0000e07a10 not found for kobject 'xgene-mii-eth0:03'
  ...
  CPU: 7 PID: 4239 Comm: reboot Tainted: G            E   4.2.0-0.18.el7.test15.aarch64 #1
  Hardware name: AppliedMicro Mustang/Mustang, BIOS 1.1.0 Aug 26 2015
  Call Trace:
  [<fffffe000009739c>] dump_backtrace+0x0/0x170
  [<fffffe000009752c>] show_stack+0x20/0x2c
  [<fffffe00007436f0>] dump_stack+0x78/0x9c
  [<fffffe00000c2cb4>] warn_slowpath_common+0xa0/0xd8
  [<fffffe00000c2d60>] warn_slowpath_fmt+0x74/0x88
  [<fffffe0000293d3c>] sysfs_remove_group+0x9c/0xa4
  [<fffffe00004a8bac>] dpm_sysfs_remove+0x5c/0x70
  [<fffffe000049b388>] device_del+0x44/0x208
  [<fffffe000049b578>] device_unregister+0x2c/0x7c
  [<fffffe000050dc68>] mdiobus_unregister+0x48/0x94
  [<fffffe000052afd0>] xgene_enet_mdio_remove+0x28/0x44
  [<fffffe000052d3f0>] xgene_enet_remove+0xd0/0xd8
  [<fffffe000052d424>] xgene_enet_shutdown+0x2c/0x3c
  [<fffffe00004a204c>] platform_drv_shutdown+0x24/0x40
  [<fffffe000049d4f4>] device_shutdown+0xf0/0x1b4
  [<fffffe00000e31ec>] kernel_restart_prepare+0x40/0x4c
  [<fffffe00000e32f8>] kernel_restart+0x1c/0x80
  [<fffffe00000e3670>] SyS_reboot+0x17c/0x250

The problem is that mdiobus_unregister() deletes the bus device before
unregistering the phy devices on the bus. This wasn't a problem before
because the phys were not children of the bus:

  /sys/devices/platform/APMC0D05:00/net/eth0/xgene-mii-eth0:03
  /sys/devices/platform/APMC0D05:00/net/eth0/xgene-mii-eth0

But now that they are:

  /sys/devices/platform/APMC0D05:00/net/eth0/xgene-mii-eth0/xgene-mii-eth0:03

when mdiobus_unregister deletes the bus device, the phy subdirs are
removed from sysfs also. So when the phys are unregistered afterward,
we get the warning. This patch changes the order so that phys are
unregistered before the bus device is deleted.

Fixes: 8b63ec18 ("phylib: Make PHYs children of their MDIO bus, not the bus' parent.")
Signed-off-by: Mark Salter <msalter@redhat.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Mark Langsdorf <mlangsdo@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>