Writing large limits resulted in overflows as reported by module tests.

in0_lcrit: Suspected overflow: [max=5538, read 0, written 2147483647]
in0_crit: Suspected overflow: [max=5538, read 0, written 2147483647]
in0_min: Suspected overflow: [max=5538, read 0, written 2147483647]

Fix the problem by clamping prior to multiplications and the use of
DIV_ROUND_CLOSEST, and by using consistent variable types.
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Fixes: f5bae264 ("hwmon: Driver for MAX16065 System Manager and compatibles")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>