ARM: dts: stm32: fix missing internally connected voltage regulator for OSD32MP1

According to the OSD32MP1 Power System overview[1] ldo3's input is always
internally connected to vdd_ddr.

[1]: https://octavosystems.com/app_notes/osd32mp1-power-system-overview/#connections



Signed-off-by: Leonard Göhrs <l.goehrs@pengutronix.de>
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>