arm64: dts: rockchip: change spi-max-frequency for Radxa ROCK 3C

SPI NOR flash chip may vary, so use safe(lowest) spi-max-frequency.

Signed-off-by: FUKAUMI Naoki <naoki@radxa.com>
Link: https://lore.kernel.org/r/20240623023329.1044-3-naoki@radxa.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>

[ upstream commit: 06f6dd4d607766a527e37529f2f3f90dd1464293 ]

(cherry picked from commit dd40945a1d0e28ae6eaf9da04f8e2dcebf8233ea)
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>