ti: sdhci: Correct voltage caps

ti,dual-volt property say that the eMMC support 1.8V and 3.3V not 3.0V
Use the correct caps for the mmc stack.
Note that the MMCHS_SD_CAPA register can only be written once after bootup
so if one is using a u-boot compiled with eMMC support (this is the default)
this code is a no-op but just in case someone have u-boot compiled without
eMMC support this make eMMC works when the kernel is booted.

MFC after: 1 week