Fix call to av1_get_rest_ntiles in restoration.c

This was getting the wrong count of restoration tiles for chroma
planes with subsampling and a smaller restoration tilesize.

BUG=aomedia:886

Change-Id: I5c9c17ed4ad91111bcc6fa6205a9550b53f84a64
diff --git a/av1/common/restoration.c b/av1/common/restoration.c
index fb47b66..00441f0 100644
--- a/av1/common/restoration.c
+++ b/av1/common/restoration.c
@@ -1799,8 +1799,8 @@
 
   int rtile_w, rtile_h, nvtiles;
   av1_get_rest_ntiles(ss_frame_w, ss_frame_h,
-                      cm->rst_info[0].restoration_tilesize, &rtile_w, &rtile_h,
-                      nhtiles, &nvtiles);
+                      cm->rst_info[plane].restoration_tilesize, &rtile_w,
+                      &rtile_h, nhtiles, &nvtiles);
 
   const int rnd_w = rtile_w * denom - 1;
   const int rnd_h = rtile_h * denom - 1;