cxgb4: fix memory leak on txq_info

Currently if txq_info->uldtxq cannot be allocated then
txq_info->txq is being kfree'd (which is redundant because it
is NULL) instead of txq_info. Fix this by instead kfree'ing
txq_info.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>