AM64 SoC, does not support HS400 and HS200 is the maximum supported speed
mode[1]. Therefore, fix the device tree node to reflect the same.

[1] - https://www.ti.com/lit/ds/symlink/am6442.pdf
      (SPRSP56C – JANUARY 2021 – REVISED FEBRUARY 2022)

Fixes: 8abae938 ("arm64: dts: ti: Add support for AM642 SoC")
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20220512064859.32059-1-a-govindraju@ti.com