change vunmapbuf to void function to match MI code

sys/arch/mvme68k/mvme68k/vm_machdep.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: vm_machdep.c,v 1.4 1996/02/05 02:10:44 christos Exp $	*/
+/*	$NetBSD: vm_machdep.c,v 1.5 1996/04/03 20:42:55 chuck Exp $	*/
 
 /*
  * Copyright (c) 1988 University of Utah.
@@ -341,6 +341,7 @@ vmapbuf(bp, sz)
  * Free the io map PTEs associated with this IO operation.
  */
 /*ARGSUSED*/
+void
 vunmapbuf(bp, sz)
 	register struct buf *bp;
 	vm_size_t sz;