ARM: dts: aspeed: wedge400: Set eMMC max frequency

Set eMMC max frequency to 25MHz to prevent intermittent eMMC access
failures.

Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20230803230324.731268-4-rentao.bupt@gmail.com


Signed-off-by: Joel Stanley <joel@jms.id.au>