microblaze/PCI: Remove useless __pci_mmap_set_pgprot()

The microblaze __pci_mmap_set_pgprot() was apparently copied from powerpc,
where it computes either an uncacheable pgprot_t or a write-combining one.
But on microblaze, we always use the regular uncacheable pgprot_t.

Remove the useless code in __pci_mmap_set_pgprot() and inline it at the
only call site.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>