net: davinci_mdio: simplify IO memory mapping

Simplify IO memory mapping by using devm_ioremap_resource()
which will do all errors handling and reporting for us.

Acked-and-tested-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>