Port of a Linux commit 4ab2e7c

  The dw_pcie_host_ops structures are never modified.  Constify these
  structures such that these can be write-protected.

  Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
  Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
  Acked-by: Jingoo Han <jingoohan1@gmail.com>
  Acked-by: Kishon Vijay Abraham I <kishon@ti.com>

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>