rtw88: fix uninitialized 'tim_offset' warning

This avoids below warning and makes compiler happy.
error: uninitialized symbol 'tim_offset'
Signed-off-by: Po-Hao Huang <phhuang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220420093058.31646-1-pkshih@realtek.com

drivers/net/wireless/realtek/rtw88/fw.c

@@ -1047,7 +1047,7 @@ static struct sk_buff *rtw_get_rsvd_page_skb(struct ieee80211_hw *hw,
 	struct rtw_vif *rtwvif;
 	struct sk_buff *skb_new;
 	struct cfg80211_ssid *ssid;
-	u16 tim_offset;
+	u16 tim_offset = 0;
 
 	if (rsvd_pkt->type == RSVD_DUMMY) {
 		skb_new = alloc_skb(1, GFP_KERNEL);