wifi: ath11k: drop NULL pointer check in ath11k_update_per_peer_tx_stats()

Since 'user_stats' is a fixed-size array of 'struct htt_ppdu_user_stats'
in 'struct htt_ppdu_stats', any of its member can't be NULL and so
relevant check may be dropped.

Found by Linux Verification Center (linuxtesting.org) with SVACE.
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230906093704.14001-1-dmantipov@yandex.ru

drivers/net/wireless/ath/ath11k/dp_rx.c

@@ -1388,9 +1388,6 @@ ath11k_update_per_peer_tx_stats(struct ath11k *ar,
 	u8 tid = HTT_PPDU_STATS_NON_QOS_TID;
 	bool is_ampdu = false;
 
-	if (!usr_stats)
-		return;
-
 	if (!(usr_stats->tlv_flags & BIT(HTT_PPDU_STATS_TAG_USR_RATE)))
 		return;