hwmon: (max6642 fix coccinelle warnings

drivers/hwmon/max6642.c:299:1-3: WARNING: PTR_RET can be used

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

Generated by: coccinelle/api/ptr_ret.cocci

CC: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>