nv30: Fix parsing of perf table

Perf tables v 1.2 and 1.3 (seen on Geforce FX/ 5) are not long enough
to store the voltage label/id

v2 - Remove comment from the code
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_perf.c

@@ -134,7 +134,7 @@ nouveau_perf_init(struct drm_device *dev)
 		case 0x13:
 		case 0x15:
 			perflvl->fanspeed = entry[55];
-			perflvl->voltage = entry[56];
+			perflvl->voltage = (recordlen > 56) ? entry[56] : 0;
 			perflvl->core = ROM32(entry[1]) * 10;
 			perflvl->memory = ROM32(entry[5]) * 20;
 			break;