rtc: stm32: Fix copyright

Uniformize STMicroelectronics copyrights header
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
CC: Amelie Delaunay <amelie.delaunay@st.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-stm32.c

 /*
- * Copyright (C) Amelie Delaunay 2016
- * Author:  Amelie Delaunay <amelie.delaunay@st.com>
+ * Copyright (C) STMicroelectronics SA 2017
+ * Author:  Amelie Delaunay <amelie.delaunay@st.com> for STMicroelectronics.
  * License terms:  GNU General Public License (GPL), version 2
  */