arm64: dts: meson: fix mmc0 tuning error on Khadas VIM3

Similar to other G12B devices using the W400 dtsi, I see reports of mmc0
tuning errors on VIM3 after a few hours uptime:

[12483.917391] mmc0: tuning execution failed: -5
[30535.551221] mmc0: tuning execution failed: -5
[35359.953671] mmc0: tuning execution failed: -5
[35561.875332] mmc0: tuning execution failed: -5
[61733.348709] mmc0: tuning execution failed: -5

I do not see the same on VIM3L, so remove sd-uhs-sdr50 from the common dtsi
to silence the error, then (re)add it to the VIM3L dts.

Fixes: 4f26cc1c ("arm64: dts: khadas-vim3: move common nodes into meson-khadas-vim3.dtsi")
Fixes: 700ab8d8

 ("arm64: dts: khadas-vim3: add support for the SM1 based VIM3L")
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20200721015950.11816-1-christianshewitt@gmail.com