lib: devres: Fix build breakage

The ERR_PTR() and IS_ERR() macros used by the devm_ioremap_resource()
function are defined in the linux/err.h header. On ARM this seems to be
pulled in by one of the other headers but the build fails at least on
OpenRISC.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>