iwlwifi: mvm: Don't call iwl_mvm_sta_from_mac80211() with NULL sta

The recent fix for NULL sta in iwl_mvm_get_tx_rate() still has a call
of iwl_mvm_sta_from_mac80211() that may be called with NULL sta.
Although this practically only points to the address and the actual
access doesn't happen due to the conditional evaluation at a later
point, it looks a bit flaky.

This patch drops the temporary variable above and evaluates
iwm_mvm_sta_from_mac80211() directly for avoiding confusions.

Fixes: d599f714 ("iwlwifi: mvm: don't crash on invalid rate w/o STA")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20220121114024.10454-1-tiwai@suse.deSigned-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/mvm/tx.c

@@ -318,15 +318,14 @@ static u32 iwl_mvm_get_tx_rate(struct iwl_mvm *mvm,
 
 	/* info->control is only relevant for non HW rate control */
 	if (!ieee80211_hw_check(mvm->hw, HAS_RATE_CONTROL)) {
-		struct iwl_mvm_sta *mvmsta = iwl_mvm_sta_from_mac80211(sta);
-
 		/* HT rate doesn't make sense for a non data frame */
 		WARN_ONCE(info->control.rates[0].flags & IEEE80211_TX_RC_MCS &&
 			  !ieee80211_is_data(fc),
 			  "Got a HT rate (flags:0x%x/mcs:%d/fc:0x%x/state:%d) for a non data frame\n",
 			  info->control.rates[0].flags,
 			  info->control.rates[0].idx,
-			  le16_to_cpu(fc), sta ? mvmsta->sta_state : -1);
+			  le16_to_cpu(fc),
+			  sta ? iwl_mvm_sta_from_mac80211(sta)->sta_state : -1);
 
 		rate_idx = info->control.rates[0].idx;
 	}