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 909b27f7, where David seems to have
lost some of the changes to iwl_mvm_set_tx_cmd() from commit
5c08b0f5 ("iwlwifi: mvm: don't override the rate with the AMSDU
len").

The reason seems to be a conflict with commit d8fe4844 ("iwlwifi:
mvm: add support for new TX CMD API"), which touched a line adjacent to
the changes in 909b27f7.

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>