arm64: dts: imx8mq-librem5: Move usdhc clocks assignment to board DT

According to commit e045f044 ("arm64: dts: imx8mq: Move usdhc clocks
assignment to board DT") add the clocks assignment to imx8mq-librem5.dtsi
too.

Fixes: e045f044

 ("arm64: dts: imx8mq: Move usdhc clocks assignment to board DT")
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>