controller_fan: Allow multiple controller_fan sections to be defined

It may be necessary to define multiple fans, so allow each config
section to be named.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extras/controller_fan.py

@@ -49,5 +49,5 @@ class ControllerFan:
         self.fan.set_speed(print_time, power)
         return eventtime + 1.
 
-def load_config(config):
+def load_config_prefix(config):
     return ControllerFan(config)