clk: stm32-h7: fix copyright

Uniformize STMicroelectronics copyrights header
Add SPDX identifier

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
CC: Gabriel Fernandez <gabriel.fernandez@st.com>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Acked-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>