hwmon: (core) Avoid ifdef CONFIG_THERMAL in C source file

hwmon: (core) Avoid ifdef CONFIG_THERMAL in C source file

Using an #ifdef in a C source files to have different definitions
of the same symbol makes the code harder to read and understand.
Furthermore it makes it harder to test compilation of the different
branches.

Replace the ifdeffery with IS_ENABLED() which is just a normal
conditional.
The resulting binary is still the same as before as the compiler
optimizes away all the unused code and definitions.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>