spi: stm32: switch to SPDX identifier

Adopt the SPDX license identifier headers to ease license compliance
management.
Signed-off-by: Cezary Gapinski <cezary.gapinski@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-stm32.c

-/*
- * STMicroelectronics STM32 SPI Controller driver (master mode only)
- *
- * Copyright (C) 2017, STMicroelectronics - All Rights Reserved
- * Author(s): Amelie Delaunay <amelie.delaunay@st.com> for STMicroelectronics.
- *
- * License terms: GPL V2.0.
- *
- * spi_stm32 driver is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 as published by
- * the Free Software Foundation.
- *
- * spi_stm32 driver is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
- * details.
- *
- * You should have received a copy of the GNU General Public License along with
- * spi_stm32 driver. If not, see <http://www.gnu.org/licenses/>.
- */
+// SPDX-License-Identifier: GPL-2.0
+//
+// STMicroelectronics STM32 SPI Controller driver (master mode only)
+//
+// Copyright (C) 2017, STMicroelectronics - All Rights Reserved
+// Author(s): Amelie Delaunay <amelie.delaunay@st.com> for STMicroelectronics.
+
 #include <linux/debugfs.h>
 #include <linux/clk.h>
 #include <linux/delay.h>