drivers: phy: constify phy_ops structures

Declare phy_ops structures as const as they are only passed as an
argument to the function devm_phy_create. This argument is of type const
struct phy_ops *, so phy_ops structures having this property can be
declared as const.
Done using Coccinelle:

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>