iwlwifi: fix length check in multi-TB HCMD

As reported by Ben Hutchings, there was a harmless issue in
the checks being done on the lengths of the TBs while
building the TFD for a multi-TB host command.

Cc: stable@vger@kernel.org
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/iwlwifi/pcie/tx.c

@@ -1264,7 +1264,7 @@ static int iwl_pcie_enqueue_hcmd(struct iwl_trans *trans,
 	for (i = 0; i < IWL_MAX_CMD_TBS_PER_TFD; i++) {
 		int copy = 0;
 
-		if (!cmd->len)
+		if (!cmd->len[i])
 			continue;
 
 		/* need at least IWL_HCMD_SCRATCHBUF_SIZE copied */