PHY: Add the phy_device_release device method.

Lately I've got this nice badness on mdio bus removal:

Device 'e0103120:06' does not have a release() function, it is broken and must be fixed.
------------[ cut here ]------------
Badness at drivers/base/core.c:107
NIP: c015c1a8 LR: c015c1a8 CTR: c0157488
REGS: c34bdcf0 TRAP: 0700   Not tainted  (2.6.23-rc5-g9ebadfbb-dirty)
MSR: 00029032 <EE,ME,IR,DR>  CR: 24088422  XER: 00000000
...
[c34bdda0] [c015c1a8] device_release+0x78/0x80 (unreliable)
[c34bddb0] [c01354cc] kobject_cleanup+0x80/0xbc
[c34bddd0] [c01365f0] kref_put+0x54/0x6c
[c34bdde0] [c013543c] kobject_put+0x24/0x34
[c34bddf0] [c015c384] put_device+0x1c/0x2c
[c34bde00] [c0180e84] mdiobus_unregister+0x2c/0x58
...

Though actually there is nothing broken, it just device
subsystem core expects another "pattern" of resource managment.

This patch implement phy device's release function, thus
we're getting rid of this badness.

Also small hidden bug fixed, hope none other introduced. ;-)

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>