RDMA/nes: Fix use-after-free in mini_cm_dec_refcnt_listen()

Fix use-after-free spotted by Coverity checker flagged by Adrian Bunk.
Signed-off-by: Faisal Latif <flatif@neteffect.com>
Signed-off-by: Glenn Streiff <gstreiff@neteffect.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/nes/nes_cm.c

@@ -947,6 +947,7 @@ static int mini_cm_dec_refcnt_listen(struct nes_cm_core *cm_core,
 		nes_debug(NES_DBG_CM, "destroying listener (%p)\n", listener);
 
 		kfree(listener);
+		listener = NULL;
 		ret = 0;
 		cm_listens_destroyed++;
 	} else {