ath9k: check pdata variable before dereferencing it

Due to my recent commit (ath9k: allow to load EEPROM
content via firmware API) smatch complains about that
the 'pdata' variable in 'ath9k_hw_init' can be NULL
and it is dereferenced before checking that. That is
absolutely correct.

Check the 'pdata' variable before using it to avoid
a NULL pointer dereference.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NGabor Juhos <juhosg@openwrt.org>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/init.c

@@ -633,7 +633,7 @@ static int ath9k_init_softc(u16 devid, struct ath_softc *sc,
 	ath_read_cachesize(common, &csz);
 	common->cachelsz = csz << 2; /* convert to bytes */
 
-	if (pdata->eeprom_name) {
+	if (pdata && pdata->eeprom_name) {
 		ret = ath9k_eeprom_request(sc, pdata->eeprom_name);
 		if (ret)
 			goto err_eeprom;