dt-bindings: mfd: stm32: Remove unnecessary blank lines

Remove double blank line.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230417181342.v2.1.I483a676579cc7e3ac07e1db649091553743fecc8@changeid