.checkpatch.conf: ignore BRACES warnings

MISRA C:2012	Rule 15.6 asks to have braces for the body of an if,
for, or while statement.
This conflicts with checkpatch, and the warning should then be ignored.

Change-Id: I22589b68b03f19a426d3bcbc10a99d4e4c76eced
Signed-off-by: Yann Gautier <yann.gautier@st.com>

.checkpatch.conf

 #
-# Copyright (c) 2016-2018, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2016-2019, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -69,3 +69,7 @@
 # "Use of volatile is usually wrong: see Documentation/volatile-considered-harmful.txt"
 # We allow the usage of the volatile keyword in TF.
 --ignore VOLATILE
+
+# BRACES reports this kind of messages:
+# braces {} are not necessary for any arm of this statement
+--ignore BRACES