The spi nor on imx8mp evk board works under SDR mode, and
driver use FlexSPIn_MCR0[RXCLKSRC] = 0x0 for SDR mode.
According to the datasheet, there is IO limitation on this chip,
the max frequency of such case is 66MHz, so add the limitation here
to align with datasheet.

Refer to 3.8.12 FlexSPI timing parameters on page 72.
https://www.nxp.com/webapp/sps/download/preDownload.jsp?render=true

Fixes: 7a2f7d763d94 ("arm64: dts: imx8mp-evk: enable fspi nor on imx8mp evk")
Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
---
 arch/arm64/boot/dts/freescale/imx8mp-evk.dts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/freescale/imx8mp-evk.dts b/arch/arm64/boot/dts/freescale/imx8mp-evk.dts
index 3730792daf5010213cbb9f6869a8110ea28eb48a..0b47d72cae9900ad53eed04c810a9ea8af795446 100644
--- a/arch/arm64/boot/dts/freescale/imx8mp-evk.dts
+++ b/arch/arm64/boot/dts/freescale/imx8mp-evk.dts
@@ -272,7 +272,7 @@ &flexspi {
 	flash@0 {
 		compatible = "jedec,spi-nor";
 		reg = <0>;
-		spi-max-frequency = <80000000>;
+		spi-max-frequency = <66000000>;
 		spi-tx-bus-width = <1>;
 		spi-rx-bus-width = <4>;
 	};

-- 
2.34.1