regulator: act8865: fix ptr_ret.cocci warnings

drivers/regulator/act8865-regulator.c:447:8-14: WARNING: PTR_ERR_OR_ZERO can be used

 Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR

Generated by: scripts/coccinelle/api/ptr_ret.cocci

Fixes: 2d09a79b

 ("regulator: act8865: Add support for act8600 charger")
CC: Maarten ter Huurne <maarten@treewalker.org>
Signed-off-by: kbuild test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20190724092236.witxtfmubun25l2t@1905cc33b6dd
Signed-off-by: Mark Brown <broonie@kernel.org>