drm/panthor: Fix panthor_devfreq kerneldoc

Missing '*' to have a valid kerneldoc prefix.
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202403031019.6jvrOqGT-lkp@intel.com/Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240304090812.3941084-2-boris.brezillon@collabora.com

drivers/gpu/drm/panthor/panthor_devfreq.c

@@ -34,7 +34,7 @@ struct panthor_devfreq {
 	/** @last_busy_state: True if the GPU was busy last time we updated the state. */
 	bool last_busy_state;
 
-	/*
+	/**
 	 * @lock: Lock used to protect busy_time, idle_time, time_last_update and
 	 * last_busy_state.
 	 *