net: stmmac: dwmac-rk: fix error path in rk_gmac_probe

Make sure we clean up devicetree related configuration
also when clock init fails.

Fixes: fecd4d7e ("net: stmmac: dwmac-rk: Add integrated PHY support")
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>