thermal: core: Remove excess empty line from a comment

The first and the third lines of the kerneldoc comment for:

thermal_zone_device_set_polling()

belong to the same sentences, so join them together.
Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/thermal/thermal_core.c

@@ -273,7 +273,6 @@ static int __init thermal_register_governors(void)
 
 /*
  * Zone update section: main control loop applied to each zone while monitoring
- *
  * in polling mode. The monitoring is done using a workqueue.
  * Same update may be done on a zone by calling thermal_zone_device_update().
  *