pinctrl: stm32: Add header with SPDX licence

Cosmetics: Add header with SPDX licence

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/drivers/pinctrl/pinctrl_stm32.c b/drivers/pinctrl/pinctrl_stm32.c
index 24ed83d..dbea995 100644
--- a/drivers/pinctrl/pinctrl_stm32.c
+++ b/drivers/pinctrl/pinctrl_stm32.c
@@ -1,3 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2017-2020 STMicroelectronics - All Rights Reserved
+ */
+
 #include <common.h>
 #include <dm.h>
 #include <hwspinlock.h>