This error indicates that the Device Tree, a data structure that tells the Linux kernel about the hardware, is missing a specific clock-frequency property.
The Pioneer FreedomBox features a dual-core ARM Cortex-A7 processor, the kernel can determine the correct clock speed for this processor through other means, so it doesn’t rely on this specific property from the Device Tree.
It doesn’t seem the error is related to hardware functionality.
Best is to ignore the error. It seems to be a known, non-critical kernel warning.