net: enetc: Use pci_release_region() to release some resources

Some resources are allocated using pci_request_region().
It is more straightforward to release them with pci_release_region().

Fixes: 231ece36 ("enetc: Add mdio bus driver for the PCIe MDIO endpoint")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>