iwlwifi: fix mis-merge that breaks the driver

My laptop that uses the intel 7680 iwlwifi module would no longer
connects to the network.  It would fail with a "Microcode SW error
detected." and spew out register state over and over again without ever
connecting to the network.

The cause is mis-merge in commit 909b27f, where David seems to have
lost some of the changes to iwl_mvm_set_tx_cmd() from commit
5c08b0f ("iwlwifi: mvm: don't override the rate with the AMSDU
len").

The reason seems to be a conflict with commit d8fe484 ("iwlwifi:
mvm: add support for new TX CMD API"), which touched a line adjacent to
the changes in 909b27f.

David missed the fact that "info->driver_data[0]" had become
"skb_info->driver_data[0]".  Then he removed the skb_info because it was
unused.

This just re-updates iwl_mvm_set_tx_cmd() with the lost two lines.

Reported-and-tested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Reinoud Koornstra <reinoudkoornstra@gmail.com>
Cc: Luciano Coelho <luciano.coelho@intel.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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

@@ -211,6 +211,7 @@ void iwl_mvm_set_tx_cmd(struct iwl_mvm *mvm, struct sk_buff *skb,
 			struct iwl_tx_cmd *tx_cmd,
 			struct ieee80211_tx_info *info, u8 sta_id)
 {
+	struct ieee80211_tx_info *skb_info = IEEE80211_SKB_CB(skb);
 	struct ieee80211_hdr *hdr = (void *)skb->data;
 	__le16 fc = hdr->frame_control;
 	u32 tx_flags = le32_to_cpu(tx_cmd->tx_flags);
@@ -294,7 +295,7 @@ void iwl_mvm_set_tx_cmd(struct iwl_mvm *mvm, struct sk_buff *skb,
 	tx_cmd->tx_flags = cpu_to_le32(tx_flags);
 	/* Total # bytes to be transmitted */
 	tx_cmd->len = cpu_to_le16((u16)skb->len +
-		(uintptr_t)info->driver_data[0]);
+		(uintptr_t)skb_info->driver_data[0]);
 	tx_cmd->life_time = cpu_to_le32(TX_CMD_LIFE_TIME_INFINITE);
 	tx_cmd->sta_id = sta_id;