hwmon: (smsc47m192) Fix overflows seen when writing into limit attributes

Module test reports overflows when writing into temperature and voltage
limit attributes

temp1_min: Suspected overflow: [127000 vs. 0]
temp1_max: Suspected overflow: [127000 vs. 0]
temp1_offset: Suspected overflow: [127000 vs. 0]
temp2_min: Suspected overflow: [127000 vs. 0]
temp2_max: Suspected overflow: [127000 vs. 0]
temp2_offset: Suspected overflow: [127000 vs. 0]
temp3_min: Suspected overflow: [127000 vs. 0]
temp3_max: Suspected overflow: [127000 vs. 0]
temp3_offset: Suspected overflow: [127000 vs. 0]
in0_min: Suspected overflow: [3320 vs. 0]
in0_max: Suspected overflow: [3320 vs. 0]
in4_min: Suspected overflow: [15938 vs. 0]
in4_max: Suspected overflow: [15938 vs. 0]
in6_min: Suspected overflow: [1992 vs. 0]
in6_max: Suspected overflow: [1992 vs. 0]
in7_min: Suspected overflow: [2391 vs. 0]
in7_max: Suspected overflow: [2391 vs. 0]

The problem is caused by conversions from unsigned long to long and
from long to int.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>