phy: bcm-ns2-pcie: Get rid of struct ns2_pci_phy

By setting phy_set_drvdata(phy, mdiodev), struct ns2_pci_phy can be
removed.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-and-tested-by: Jon Mason <jon.mason@broadcom.com>
Reviewed-by: Pramod Kumar <pramodku@broadcom.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>