ssc100_common
err = ssc100_common(unitp, byte, reg, I2C_WR_RD);
err = ssc100_common(unitp, byte, 0, I2C_RD);
err = ssc100_common(unitp, NULL, byte, I2C_WR);
static int ssc100_common(struct ssc100_unit *, uchar_t *, uchar_t, int8_t);