SPM: Avoid null ptr reference

Null ptr reference introduced in commit ef42f444063280f217cc4bcfc4fb43bfa4df8932
"SPM: Stateless services can be searched by sid"

Change-Id: I8ef7e1945605b9ecbeaaa78fbf3179088183844b
Signed-off-by: Raymond Ngun <raymond.ngun@infineon.com>
diff --git a/secure_fw/spm/cmsis_psa/spm_ipc.c b/secure_fw/spm/cmsis_psa/spm_ipc.c
index 359bfac..7f4bc2f 100644
--- a/secure_fw/spm/cmsis_psa/spm_ipc.c
+++ b/secure_fw/spm/cmsis_psa/spm_ipc.c
@@ -330,8 +330,10 @@
     struct service_t *p_serv = connection_services_listhead;
 
     for (i = 0; i < STATIC_HANDLE_NUM_LIMIT; i++) {
-        if (stateless_services_ref_tbl[i]->p_ldinf->sid == sid) {
-            return stateless_services_ref_tbl[i];
+        if (stateless_services_ref_tbl[i]) {
+            if (stateless_services_ref_tbl[i]->p_ldinf->sid == sid) {
+                return stateless_services_ref_tbl[i];
+            }
         }
     }