ath10k: htt: remove some dead code

We added an unnecessary condition here in commit a904417f ("ath10k:
add extended per sta tx statistics support").  "legacy_rate_idx" is a u8
so it can't be negative.  The caller doesn't pass negatives either.  I
have deleted this code.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/ath10k/htt_rx.c

@@ -2680,8 +2680,6 @@ ath10k_accumulate_per_peer_tx_stats(struct ath10k *ar,
 		STATS_OP_FMT(RETRY).ht[1][ht_idx] += pstats->retry_pkts;
 	} else {
 		mcs = legacy_rate_idx;
-		if (mcs < 0)
-			return;
 
 		STATS_OP_FMT(SUCC).legacy[0][mcs] += pstats->succ_bytes;
 		STATS_OP_FMT(SUCC).legacy[1][mcs] += pstats->succ_pkts;