wm_sfp_read_data_byte
static int wm_sfp_read_data_byte(struct wm_softc *, uint16_t, uint8_t *);
rv = wm_sfp_read_data_byte(sc, SFF_SFP_ID_OFF, &val);
rv = wm_sfp_read_data_byte(sc, SFF_SFP_ETH_FLAGS_OFF, &val);