rtw89: fix uninitialized variable of rtw89_append_probe_req_ie()

smatch reports that:
  fw.c:1997 rtw89_append_probe_req_ie() error: uninitialized symbol 'ret'.

This can be a issue only if no band is supported by the chip, but it is
impossible. So, it is still safe without this patch.
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220311020007.20414-1-pkshih@realtek.com

drivers/net/wireless/realtek/rtw89/fw.c

@@ -1964,7 +1964,7 @@ static int rtw89_append_probe_req_ie(struct rtw89_dev *rtwdev,
 	struct ieee80211_scan_ies *ies = rtwvif->scan_ies;
 	struct rtw89_pktofld_info *info;
 	struct sk_buff *new;
-	int ret;
+	int ret = 0;
 	u8 band;
 
 	for (band = NL80211_BAND_2GHZ; band < NUM_NL80211_BANDS; band++) {