common: avb_verify: prevent opening incorrect session

The arg->session is not valid if arg->ret != NULL, so can't be
assigned, correct this.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@globallogic.com>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/common/avb_verify.c b/common/avb_verify.c
index 0520a71..48ba8db 100644
--- a/common/avb_verify.c
+++ b/common/avb_verify.c
@@ -619,10 +619,11 @@
 		memset(&arg, 0, sizeof(arg));
 		tee_optee_ta_uuid_to_octets(arg.uuid, &uuid);
 		rc = tee_open_session(tee, &arg, 0, NULL);
-		if (!rc) {
-			ops_data->tee = tee;
-			ops_data->session = arg.session;
-		}
+		if (rc || arg.ret)
+			continue;
+
+		ops_data->tee = tee;
+		ops_data->session = arg.session;
 	}
 
 	return 0;