hwmon: (dell-smm-hwmon) Move variables into a driver private data structure

Move Variables into a driver private data structure.
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20210728221557.8891-5-W_Armin@gmx.deSigned-off-by: Guenter Roeck <linux@roeck-us.net>