net: mv643xx_eth: disable clk on error path in mv643xx_eth_shared_probe()

If mv643xx_eth_shared_of_probe() fails, mv643xx_eth_shared_probe()
leaves clk enabled.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>