TF-M patch: Fix service handles not cleared issue (TF-M issue ARMmbed#230)

- Link to bug tracking: https://developer.trustedfirmware.org/T230

Author: Michael Schwarcz

components/TARGET_PSA/TARGET_TFM/COMPONENT_SPE/secure_fw/core/ipc/tfm_spm.c

@@ -108,6 +108,8 @@ int32_t tfm_spm_free_conn_handle(struct tfm_spm_service_t *service,
     /* Remove node from handle list */
     tfm_list_del_node(&node->list);
 
+    node->rhandle = NULL;
+
     /* Back handle buffer to pool */
     tfm_pool_free(node);
     return IPC_SUCCESS;