rtc: stm32: fix copyright and adopt SPDX identifier

Fix copyright by removing "SA" and "for STMicroelectronics", not required.
Adopt SPDX identifier.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
1 file changed