net: ethernet: ti: davinci_mdio: use devm_ioremap()

The Davinci MDIO in most of the case implemented as module inside of TI
CPSW subsystem and fully depends on CPSW to be enabled, but historically
it's implemented as separate Platform device/driver and defined in DT files
in two ways:
- as standalone node
- as child node of CPSW subsystem.

In later case it's required to split CPSW subsystem "reg" property to
exclude MDIO I/O range which is not useful.

Hence, replace devm_ioremap_resource() with devm_ioremap() to allow define
full I/O range in parent CPSW subsystem without spliting.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>