Silent compiler warning of unused variable

Change-Id: I1b921e79484e78a272c4f62e30cb85631a65ac25

av1/encoder/pickrst.c

diff --git a/av1/encoder/pickrst.c b/av1/encoder/pickrst.c
index 0ec6f30..e530137 100644
--- a/av1/encoder/pickrst.c
+++ b/av1/encoder/pickrst.c
@@ -364,6 +364,9 @@
          pu_width == RESTORATION_PROC_UNIT_SIZE);
   assert(pu_height == (RESTORATION_PROC_UNIT_SIZE >> 1) ||
          pu_height == RESTORATION_PROC_UNIT_SIZE);
+#if !CONFIG_HIGHBITDEPTH
+  (void)bit_depth;
+#endif
 
   for (ep = 0; ep < SGRPROJ_PARAMS; ep++) {
     int exq[2];