PCI: hisi: Remove unused variable driver

The local "driver" variable was unused and caused a warning, so remove it:

  drivers/pci/dwc/pcie-hisi.c: In function 'hisi_pcie_probe':
  drivers/pci/dwc/pcie-hisi.c:271:24: warning: variable 'driver' set but not used [-Wunused-but-set-variable]

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Zhou Wang <wangzhou1@hisilicon.com>
Acked-by: Gabriele Paoloni <gabriele.paoloni@huawei.com>