dts: arm: st: fix SDMMC2 for the H7 family

The different references manuals of the STM32H7 family (RM099, RM0433,
RM0445 and RM0468) states that SDMMC2RTS and STMMC2EN are on bit 9 of
respectively RCC_AHB2RSTR and RCC_AHB2ENR (not on bit 8). Fixes the stm32h7
dts accordingly.

Signed-off-by: Johan Lafon <johan.lafon@syslinbit.com>