arm64: dts: imx8mq-librem5: Limit the max sdio frequency

This is needed for the 1LV Cyress WiFi module to probe correctly.
It also helps improve GNSS sensitivity.

Signed-off-by: Angus Ainslie <angus@akkea.ca>
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>