ia64: Remove redundant checks for WC in pci_mmap_page_range()

For a PCI MMIO BAR, phys_mem_access_prot() should always return UC or WC.
And while a mixture of cached and uncached mappings is forbidden, we were
already mixing WC and UC, which is OK. Just do as we're asked.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Tested-by: Tony Luck <tony.luck@intel.com>