bnx2x: remove not necessary compiler barrier

Access to fp->tx_bd_prod is protected by __netif_tx_lock, so we do not
need any barrier for that.

Update of fp->tx_bd_cons in bnx2x_tx_int() is not protected by lock, but
barrier() nor smb_mb() in bnx2x_tx_avail() not guarantee we will see
values that is written on other cpu. Ordering issues between
netif_tx_stop_queue(), netif_tx_queue_stopped(), fp->tx_bd_cons = bd_cons
and bnx2x_tx_avail() are already handled by smp_mb() in bnx2x_tx_int()
and bnx2x_start_xmit().

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>