The CSI1 PHY reference clock is limited to 125 MHz according to:
i.MX 8M Mini Applications Processor Reference Manual, Rev. 3, 11/2020
Table 5-1. Clock Root Table (continued) / page 307
Slice Index n = 123 .

Currently the IMX8MM_CLK_CSI1_PHY_REF clock is configured to be
fed directly from 1 GHz PLL2 , which overclocks them. Instead, drop
the configuration altogether, which defaults the clock to 24 MHz REF
clock input, which for the PHY reference clock is just fine.

Based on a patch from Marek Vasut for the imx8mn.

Fixes: e523b7c5 ("arm64: dts: imx8mm: Add CSI nodes")
Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>