stm32mp: stm32prog: Normalise newlines

The missing trailing newline could confuse check-config.sh if the
definition of an option was on the first line of the next file that
find(1) happened to return.

Signed-off-by: William Grant <wgrant@ubuntu.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>