RMDA/cm: Fix missing ib_cm_destroy_id() in ib_cm_insert_listen()

The algorithm pre-allocates a cm_id since allocation cannot be done while
holding the cm.lock spinlock, however it doesn't free it on one error
path, leading to a memory leak.

Fixes: 067b171b86 ("IB/cm: Share listening CM IDs")
Link: https://lore.kernel.org/r/20200221152023.GA8680@ziepe.ca
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/cm.c

@@ -1191,6 +1191,7 @@ struct ib_cm_id *ib_cm_insert_listen(struct ib_device *device,
 			/* Sharing an ib_cm_id with different handlers is not
 			 * supported */
 			spin_unlock_irqrestore(&cm.lock, flags);
+			ib_destroy_cm_id(cm_id);
 			return ERR_PTR(-EINVAL);
 		}
 		refcount_inc(&cm_id_priv->refcount);