Revert "net: bcmgenet: Ensure MDIO unregistration has clocks enabled"

This reverts commit 1b5ea7ff ("net:
bcmgenet: Ensure MDIO unregistration has clocks enabled"). This is no
longer necessary now that the MDIO bus controller has a clock that it
can manage around the I/O accesses.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>