arm64: dts: imx8mm-verdin: update CAN clock to 40MHz

Update SPI CAN controller clock to match current hardware design.

Signed-off-by: Andrejs Cainikovs <andrejs.cainikovs@toradex.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Fixes: 6a57f224 ("arm64: dts: freescale: add initial support for verdin imx8m mini")
Signed-off-by: Shawn Guo <shawnguo@kernel.org>