thermal/intel_powerclamp: Remove duplicated code that starts the kthread

This patch removes code duplication. It does not modify
the functionality.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>