Wrap pgprot_t initializer with __pgprot() to comply with the
STRICT_MM_TYPECHECKS rules.

[bhelgaas: changelog]
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Thierry Reding <treding@nvidia.com>