x86, mtrr: Use pci_dev->revision

This code uses PCI_CLASS_REVISION instead of PCI_REVISION_ID, so
it wasn't converted by commit 44c10138fd4 ("PCI: Change all
drivers to use pci_device->revision") before being moved to
arch/x86/...

Do it now at last -- and save one level of indentation...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/201107012242.08347.sshtylyov@ru.mvista.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>