arm64: dts: imx8mn: Drop CSI1 PHY reference clock configuration

The CSI1 PHY reference clock are limited to 125 MHz according to:
i.MX 8M Nano Applications Processor Reference Manual, Rev. 2, 07/2022
Table 5-1. Clock Root Table (continued) / page 319
Slice Index n = 123 .

Currently those IMX8MN_CLK_CSI1_PHY_REF clock are 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.

Fixes: ae9279f3 ("arm64: dts: imx8mn: Add CSI and ISI Nodes")
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>