Fix YUV444 lossless mode unit test

Properly scale the chroma component size per color plane.

Change-Id: Ibf192d0e99f2fc3611beb82a3a9951ad09b292d3
diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index c00c3d2..cbed979 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -3754,7 +3754,9 @@
 
 #if CONFIG_CB4X4 && !CONFIG_CHROMA_2X2
   if (x->skip_chroma_rd) return is_cost_valid;
-  bsize = AOMMAX(BLOCK_8X8, bsize);
+
+  bsize = scale_chroma_bsize(bsize, xd->plane[1].subsampling_x,
+                             xd->plane[1].subsampling_y);
 #endif  // CONFIG_CB4X4 && !CONFIG_CHROMA_2X2
 
 #if !CONFIG_PVQ