x86: remove set_fixmap() warning

set_fixmap()+clear_fixmap() is safe.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 7a81dd0..b798e7b 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -173,7 +173,7 @@
 	new_pte = pfn_pte(phys >> PAGE_SHIFT, prot);
 
 	pte = pte_offset_kernel(pmd, vaddr);
-	if (!pte_none(*pte) &&
+	if (!pte_none(*pte) && pte_val(new_pte) &&
 	    pte_val(*pte) != (pte_val(new_pte) & __supported_pte_mask))
 		pte_ERROR(*pte);
 	set_pte(pte, new_pte);