net: ethernet: stmmac: dwmac-meson8b: fix probe error path

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

Fixes: 566e8251 ("net: stmmac: add a glue driver for the Amlogic
Meson 8b / GXBB DWMAC")
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>