Use an int to calculate scale values inside scmi_hwmon_scale() to match
the updated scale data type in struct scmi_sensor_info.

Link: https://lore.kernel.org/r/20201119174906.43862-4-cristian.marussi@arm.com
Cc: linux-hwmon@vger.kernel.org
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>