RPC: properly handle the semaphore in error case

This is to fix below issue:
https://github.com/spdk/spdk/issues/1076

The problem is that the semaphore is not increased and
the wait operation time out.

Change-Id: I56e950d0705663b35de9257f17c400c31636ee34
Signed-off-by: GangCao <gang.cao@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/476048
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Liang Yan <liang.z.yan@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>

test/rpc_client/rpc_client_test.c

@@ -338,6 +338,7 @@ rpc_server_th(void *arg)
 	rc = spdk_rpc_listen(g_rpcsock_addr);
 	if (rc) {
 		fprintf(stderr, "spdk_rpc_listen() failed: %d\n", rc);
+		sem_post(&g_rpc_server_th_listening);
 		goto out;
 	}