hwmon: (lm63) Fix smatch warnings

smatch complains as follows when checking lm63.c.

drivers/hwmon/lm63.c:594 set_temp11() warn:
		'65504' 65504 can't fit into 32767 'data->temp11[nr]'
drivers/hwmon/lm63.c:596 set_temp11() warn:
		'32768' 32768 can't fit into 32767 'data->temp11[nr]'

Fix by using DIV_ROUND_CLOSEST and clamp_val to convert the values.
While we are at it, modify other macros as well for consistency and
to make the code easier to understand.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>