cpuidle-kirkwood.c: simplify use of devm_ioremap_resource()

Remove unneeded error handling on the result of a call to
platform_get_resource when the value is passed to
devm_ioremap_resource().

A simplified version of the semantic patch that makes this change is
as follows: (http://coccinelle.lip6.fr/

)

// <smpl>
@@
expression pdev,res,n,e,e1;
expression ret != 0;
identifier l;
@@

- res = platform_get_resource(pdev, IORESOURCE_MEM, n);
  ... when != res
- if (res == NULL) { ... \(goto l;\|return ret;\) }
  ... when != res
+ res = platform_get_resource(pdev, IORESOURCE_MEM, n);
  e = devm_ioremap_resource(e1, res);
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>