cxgb4: unnecessary check for 0 in the free_sge_txq_uld() function

The free_sge_txq_old() function has an unnecessary txq check of 0.
This check is not necessary, since the txq pointer is initialized by the
uldtxq[i] address from the operation &txq_info->uldtxq[i], which ensures
that txq is not equal to 0.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: ab677ff4

 ("cxgb4: Allocate Tx queues dynamically")
Signed-off-by: Mikhail Lobanov <m.lobanov@rosalinux.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>