phy: Don't increment MDIO bus refcount unless it's a different owner

phy: Don't increment MDIO bus refcount unless it's a different owner

Commit 2a4b2f490295 ("phy: fix mdiobus module safety") fixed the way we
dealt with MDIO bus module reference count, but sort of introduced a
regression in that, if an Ethernet driver registers its own MDIO bus
driver, as is common, we will end up with the Ethernet driver's
module->refnct set to 1, thus preventing this driver from any removal.

Fix this by comparing the network device's device driver owner against
the MDIO bus driver owner, and only if they are different, increment the
MDIO bus module refcount.

Fixes: 2a4b2f490295 ("phy: fix mdiobus module safety")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>