x86: rename PTE_MASK to PTE_PFN_MASK

Rusty, in his peevish way, complained that macros defining constants
should have a name which somewhat accurately reflects the actual
purpose of the constant.

Aside from the fact that PTE_MASK gives no clue as to what's actually
being masked, and is misleadingly similar to the functionally entirely
different PMD_MASK, PUD_MASK and PGD_MASK, I don't really see what the
problem is.

But if this patch silences the incessent noise, then it will have
achieved its goal (TODO: write test-case).

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/asm-x86/xen/page.h b/include/asm-x86/xen/page.h
index 05e678a..7b3835d 100644
--- a/include/asm-x86/xen/page.h
+++ b/include/asm-x86/xen/page.h
@@ -124,7 +124,7 @@
 
 static inline unsigned long pte_mfn(pte_t pte)
 {
-	return (pte.pte & PTE_MASK) >> PAGE_SHIFT;
+	return (pte.pte & PTE_PFN_MASK) >> PAGE_SHIFT;
 }
 
 static inline pte_t mfn_pte(unsigned long page_nr, pgprot_t pgprot)