ARM: dts: stm32: fix the Odyssey SoM eMMC VQMMC supply

The Seeed SoM-STM32MP157C device tree had the eMMC’s (SDMMC2) VQMMC
supply set to v3v3 (buck4), the same as the VMMC supply. That was
incorrect, as on the SoM, the VQMMC supply is provided from vdd (buck3)
instead.

Signed-off-by: Grzegorz Szymaszek <gszymaszek@short.pl>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>