block, bfq: fix comments on __bfq_deactivate_entity

Comments on function __bfq_deactivate_entity contains two imprecise or
wrong statements:
1) The function performs the deactivation of the entity.
2) The function must be invoked only if the entity is on a service tree.

This commits replaces both statements with the correct ones:
1) The functions updates sched_data and service trees for the entity,
so as to represent entity as inactive (which is only part of the steps
needed for the deactivation of the entity).
2) The function must be invoked on every entity being deactivated.
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bfq-wf2q.c

@@ -1154,15 +1154,14 @@ static void bfq_activate_requeue_entity(struct bfq_entity *entity,
 }
 
 /**
- * __bfq_deactivate_entity - deactivate an entity from its service tree.
- * @entity: the entity to deactivate.
+ * __bfq_deactivate_entity - update sched_data and service trees for
+ * entity, so as to represent entity as inactive
+ * @entity: the entity being deactivated.
  * @ins_into_idle_tree: if false, the entity will not be put into the
  *			idle tree.
  *
- * Deactivates an entity, independently of its previous state.  Must
- * be invoked only if entity is on a service tree. Extracts the entity
- * from that tree, and if necessary and allowed, puts it into the idle
- * tree.
+ * If necessary and allowed, puts entity into the idle tree. NOTE:
+ * entity may be on no tree if in service.
  */
 bool __bfq_deactivate_entity(struct bfq_entity *entity, bool ins_into_idle_tree)
 {