net: ethernet: stmmac: dwmac-sti: fix probe error path

Make sure to disable clocks before returning on late probe errors.

Fixes: 8387ee21 ("stmmac: dwmac-sti: turn setup callback into a
probe function")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>