pwm: stm32: Adopt SPDX identifier

Add SPDX identifier to make it easier to determine the license of the
file.
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Acked-by: Philippe Ombredanne <pombredanne@nexb.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-stm32-lp.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * STM32 Low-Power Timer PWM driver
  *
@@ -5,8 +6,6 @@
  *
  * Author: Gerald Baeza <gerald.baeza@st.com>
  *
- * License terms: GNU General Public License (GPL), version 2
- *
  * Inspired by Gerald Baeza's pwm-stm32 driver
  */
 

drivers/pwm/pwm-stm32.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) STMicroelectronics 2016
  *
  * Author: Gerald Baeza <gerald.baeza@st.com>
  *
- * License terms: GNU General Public License (GPL), version 2
- *
  * Inspired by timer-stm32.c from Maxime Coquelin
  *             pwm-atmel.c from Bo Shen
  */