Similar to what was done for the lm75 driver.

Add depends on THERMAL since that is what provides the
register/unregister functions above, but only if THERMAL_OF was
selected as this is an optional feature of the driver.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Eduardo Valentin <eduardo.valentin@ti.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>