drm/radeon/kms: fix tracking of BLENDCNTL, COLOR_CHANNEL_MASK, and GB_Z on r300

Also move ZB_DEPTHCLEARVALUE to the list of safe regs.

Signed-off-by: Marek Olšák <maraeo@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/r300.c b/drivers/gpu/drm/radeon/r300.c
index 15f9464..862b617 100644
--- a/drivers/gpu/drm/radeon/r300.c
+++ b/drivers/gpu/drm/radeon/r300.c
@@ -873,6 +873,7 @@
 		track->zb_dirty = true;
 		break;
 	case 0x4104:
+		/* TX_ENABLE */
 		for (i = 0; i < 16; i++) {
 			bool enabled;
 
@@ -1103,8 +1104,6 @@
 		track->blend_read_enable = !!(idx_value & (1 << 2));
 		track->cb_dirty = true;
 		break;
-	case 0x4f28: /* ZB_DEPTHCLEARVALUE */
-		break;
 	case 0x4f30: /* ZB_MASK_OFFSET */
 	case 0x4f34: /* ZB_ZMASK_PITCH */
 	case 0x4f44: /* ZB_HIZ_OFFSET */