KVM: do not release the error page

After commit a2766325cf9f9, the error page is replaced by the
error code, it need not be released anymore

[ The patch has been compiling tested for powerpc ]

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 56f5533..ea475cd 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -111,7 +111,7 @@
 			list_entry(vcpu->async_pf.done.next,
 				   typeof(*work), link);
 		list_del(&work->link);
-		if (work->page)
+		if (!is_error_page(work->page))
 			kvm_release_page_clean(work->page);
 		kmem_cache_free(async_pf_cache, work);
 	}
@@ -138,7 +138,7 @@
 
 		list_del(&work->queue);
 		vcpu->async_pf.queued--;
-		if (work->page)
+		if (!is_error_page(work->page))
 			kvm_release_page_clean(work->page);
 		kmem_cache_free(async_pf_cache, work);
 	}