ipw_read_prom_word
val = ipw_read_prom_word(sc, IPW_EEPROM_MAC + 0);
val = ipw_read_prom_word(sc, IPW_EEPROM_MAC + 1);
val = ipw_read_prom_word(sc, IPW_EEPROM_MAC + 2);
uint16_t ipw_read_prom_word(struct ipw_softc *, uint8_t);