drm/nouveau/bios/iccsense: rails for power sensors have a mask of 0xf8 for version 0x10

I only saw those values inside the vbios: 0xff, 0xfd, 0xfc, 0xfa for valid
rails.

No idea what the lower value does, but at least we get power readings on
a lot of Fermi GPUs with that.

v2: add missing parentheses
Signed-off-by: Karol Herbst <karolherbst@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nvkm/subdev/bios/iccsense.c

@@ -87,7 +87,10 @@ nvbios_iccsense_parse(struct nvkm_bios *bios, struct nvbios_iccsense *iccsense)
 
 		switch(ver) {
 		case 0x10:
-			rail->mode = nvbios_rd08(bios, entry + 0x1);
+			if ((nvbios_rd08(bios, entry + 0x1) & 0xf8) == 0xf8)
+				rail->mode = 1;
+			else
+				rail->mode = 0;
 			rail->extdev_id = nvbios_rd08(bios, entry + 0x2);
 			res_start = 0x3;
 			break;