mempool: clarify enqueue/dequeue ops documentation

API documentations doesn't clarify expected return types for enqueue and
dequeue mempool_ops, clarifying it.

Fixes: 449c49b ("mempool: support handler operations")
Cc: stable@dpdk.org

Reported-by: Morten Brørup <mb@smartsharesystems.com>
Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
Reviewed-by: Morten Brørup <mb@smartsharesystems.com>

lib/mempool/rte_mempool.h

@@ -465,13 +465,19 @@ typedef int (*rte_mempool_alloc_t)(struct rte_mempool *mp);
 typedef void (*rte_mempool_free_t)(struct rte_mempool *mp);
 
 /**
- * Enqueue an object into the external pool.
+ * Enqueue 'n' objects into the external pool.
+ * @return
+ *   - 0: Success
+ *   - <0: Error
  */
 typedef int (*rte_mempool_enqueue_t)(struct rte_mempool *mp,
 		void * const *obj_table, unsigned int n);
 
 /**
- * Dequeue an object from the external pool.
+ * Dequeue 'n' objects from the external pool.
+ * @return
+ *   - 0: Success
+ *   - <0: Error
  */
 typedef int (*rte_mempool_dequeue_t)(struct rte_mempool *mp,
 		void **obj_table, unsigned int n);