PCI: spear13xx: Avoid invalid address space conversions

The sparse checker complains about converting pointers between address
spaces.  We correctly stored an __iomem pointer in struct spear13xx_pcie,
but discarded the __iomem when extracting app_base, causing one warning.
Then we passed the non-__iomem pointer to writel(), which expects an
__iomem pointer, causing another warning.

Add the appropriate annotations.

The sparse warnings look like this:

  $ make C=2 drivers/pci/controller/
  drivers/pci/controller/dwc/pcie-spear13xx.c:72:54: warning: incorrect type in initializer (different address spaces)
  drivers/pci/controller/dwc/pcie-spear13xx.c:72:54:    expected struct pcie_app_reg *app_reg
  drivers/pci/controller/dwc/pcie-spear13xx.c:72:54:    got void [noderef] __iomem *app_base
  drivers/pci/controller/dwc/pcie-spear13xx.c:78:26: warning: incorrect type in argument 2 (different address spaces)
  drivers/pci/controller/dwc/pcie-spear13xx.c:78:26:    expected void volatile [noderef] __iomem *addr
  drivers/pci/controller/dwc/pcie-spear13xx.c:78:26:    got unsigned int *

Link: https://lore.kernel.org/r/20211223213749.1314142-3-helgaas@kernel.org
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Pratyush Anand <pratyush.anand@gmail.com>