Core: Fix the access to service signal

Service is a array variable and access to element
should be using through array index.

Signed-off-by: Jaykumar Pitambarbhai Patel <jaykumar.pitambarbhaipatel@arm.com>
Change-Id: I607d69202ff67e78810a490a462c94ec53fbbcb4
diff --git a/secure_fw/spm/spm_api_ipc.c b/secure_fw/spm/spm_api_ipc.c
index 80b4351..cca156e 100644
--- a/secure_fw/spm/spm_api_ipc.c
+++ b/secure_fw/spm/spm_api_ipc.c
@@ -605,7 +605,7 @@
             tfm_core_panic();
         }
         service[i].partition = partition;
-        partition->runtime_data.assigned_signals |= service->service_db->signal;
+        partition->runtime_data.assigned_signals |= service[i].service_db->signal;
 
         tfm_list_init(&service[i].handle_list);
         tfm_list_add_tail(&partition->runtime_data.service_list,