rtw88: check for validity before using a pointer

rtw88: check for validity before using a pointer

[ Upstream commit a12f809968dbf46ce2a6bc94463db8d431bb75fc ]

ieee80211_probereq_get() can return NULL. Pointer skb should be checked
for validty before use. If it is not valid, list of skbs needs to be
freed.

Fixes: 10d162b2ed39 ("rtw88: 8822c: add ieee80211_ops::hw_scan")
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220121070813.9656-2-pkshih@realtek.com
Signed-off-by: Sasha Levin <sashal@kernel.org>