SCLK_SDMMC is the parent for SCLK_SDMMC_DRV and SCLK_SDMMC_SAMPLE, but
used with the (more) correct name sclk_sdmmc. SD card tuning does currently
fail as the parent can't be found under that name.
There is no need to suffix the name with '0' since RK312x SoCs do have a
single sdmmc controller - so rename it to the name which is already used
by it's children.