cxgb4vf: Remove superfluous call to pci_disable_msix()

There is no need to call pci_disable_msix() in case
the previous call to pci_enable_msix() failed

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Cc: Casey Leedom <leedom@chelsio.com>
Cc: netdev@vger.kernel.org
Cc: linux-pci@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>