mtd: nand: pxa3xx: Use devm_ioremap_resource

Using the new devm_ioremap_resource() we can greatly
simplify resource handling.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>