Change assert(1) to assert(0).

This issue was introduced in commit bf0b45a089d8b775236b3ab3a7cfc3d78dda39c1.

BUG=aomedia:2426

Change-Id: I6bd22eec90739475386be59e1ef4c2bdffde9262
diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index 1855200..e3f4099 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -8205,7 +8205,7 @@
       this_rd_stats = *rd_stats;
       break;
     case INTERP_EVAL_INVALID:
-    default: assert(1); return 0;
+    default: assert(0); return 0;
   }
   int64_t tmp_rd =
       RDCOST(x->rdmult, tmp_rs + this_rd_stats.rate, this_rd_stats.dist);