Fix the error of crashing when sending multiple characters via cdc

[Steffen-W]

Fixes the problem of buffer processing.

Correction affects the function size_t CDCusb::write(const uint8_t *buffer, size_t size)

Crashes due to the use of this function are avoided. Likewise, crashing due to the use of printf is avoided. This function uses CDCusb::write. Please merge.