libceph: use kvfree() instead of open-coding it

This one sneaked in through vfs tree with commit 2b777c9dd9eb
("ceph_sync_read: stop poking into iov_iter guts").

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
diff --git a/net/ceph/pagevec.c b/net/ceph/pagevec.c
index 096d914..d4f5f22 100644
--- a/net/ceph/pagevec.c
+++ b/net/ceph/pagevec.c
@@ -51,10 +51,7 @@
 			set_page_dirty_lock(pages[i]);
 		put_page(pages[i]);
 	}
-	if (is_vmalloc_addr(pages))
-		vfree(pages);
-	else
-		kfree(pages);
+	kvfree(pages);
 }
 EXPORT_SYMBOL(ceph_put_page_vector);