KVM: do not treat noslot pfn as a error pfn

This patch filters noslot pfn out from error pfns based on Marcelo comment:
noslot pfn is not a error pfn

After this patch,
- is_noslot_pfn indicates that the gfn is not in slot
- is_error_pfn indicates that the gfn is in slot but the error is occurred
  when translate the gfn to pfn
- is_error_noslot_pfn indicates that the pfn either it is error pfns or it
  is noslot pfn
And is_invalid_pfn can be removed, it makes the code more clean

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index d17deca..891eb6d 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -323,7 +323,7 @@
 	protect_clean_gpte(&pte_access, gpte);
 	pfn = pte_prefetch_gfn_to_pfn(vcpu, gfn,
 			no_dirty_log && (pte_access & ACC_WRITE_MASK));
-	if (is_invalid_pfn(pfn))
+	if (is_error_pfn(pfn))
 		return false;
 
 	/*