firei2c_clock
sc->sc_i2c_clks[FIREI2C_CLK_FULL] = firei2c_clock(sysclk);
sc->sc_i2c_clks[FIREI2C_CLK_HALF] = firei2c_clock(sysclk / 2);
sc->sc_i2c_clks[FIREI2C_CLK_TT] = firei2c_clock(sysclk / 32);
static uint8_t firei2c_clock(int);