Make it work better when there is no slit.

Reference: /n/patches.lsub.org/patch/slitless
Date: Mon Jun 25 16:30:42 CES 2012
Signed-off-by: paurea@lsub.org

--- /sys/src/nix/k10/devacpi.c	Tue May 22 16:10:12 2012
+++ /sys/src/nix/k10/devacpi.c	Mon Jun 25 16:29:11 2012
@@ -876,7 +876,7 @@
 	int ncorepercol;
 
 	if(slit == nil)
-		return 0;
+		return index;
 	ncorepercol = MACHMAX/slit->rowlen;
 	color = slit->e[mycolor][index/ncorepercol].dom;
 	return color * ncorepercol + index % ncorepercol;