umcs7840_calc_baudrate
if (umcs7840_calc_baudrate(rate, &divisor, &clk)) {
static usb_error_t umcs7840_calc_baudrate(uint32_t rate, uint16_t *, uint8_t *);
if (umcs7840_calc_baudrate(t->c_ospeed, &divisor, &clk) || !divisor)