staging: mt7621-dts: update sdhci config.

The mtk-sd driver has been updated to support
the IP in the mt7621, so update our configuration
to work with it.

Signed-off-by: NeilBrown <neil@brown.name>
Link: https://lore.kernel.org/r/156194178761.1430.1625105851941268306.stgit@noble.brown


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>