fix(tsp): fix destination ID in direct request

Ensure the TSP ID is set as the source ID in a direct request.

Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>
Change-Id: Ia082fe5a1da6f2994072ec70c6ba818212a52f20
diff --git a/bl32/tsp/tsp_ffa_main.c b/bl32/tsp/tsp_ffa_main.c
index 268d329..1c8c68f 100644
--- a/bl32/tsp/tsp_ffa_main.c
+++ b/bl32/tsp/tsp_ffa_main.c
@@ -91,7 +91,7 @@
 	smc_args_t ffa_forward_result;
 	ffa_endpoint_id16_t receiver = arg5;
 
-	ffa_forward_result = ffa_msg_send_direct_req(ffa_endpoint_source(arg1),
+	ffa_forward_result = ffa_msg_send_direct_req(tsp_id,
 						     receiver,
 						     FF_A_ECHO_MESSAGE, arg4,
 						     0, 0, 0);