regulator: max8660: fix build warnings

Fix a build warning for !CONFIG_OF and a cast from void* to
unsigned int which is invalid on 64bit machines.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>