av1_update_film_grain_parameters: add missing alloc check

+ convert malloc+memset to calloc

Bug: aomedia:3276
Change-Id: Ic9075501e8e6ea2af30f8bd334d9c92297458f5b
diff --git a/av1/encoder/encoder_utils.c b/av1/encoder/encoder_utils.c
index 02a7e59..c8f6085 100644
--- a/av1/encoder/encoder_utils.c
+++ b/av1/encoder/encoder_utils.c
@@ -658,8 +658,8 @@
       }
     }
   } else if (tune_cfg->film_grain_table_filename) {
-    cpi->film_grain_table = aom_malloc(sizeof(*cpi->film_grain_table));
-    memset(cpi->film_grain_table, 0, sizeof(aom_film_grain_table_t));
+    CHECK_MEM_ERROR(cm, cpi->film_grain_table,
+                    aom_calloc(1, sizeof(*cpi->film_grain_table)));
 
     aom_film_grain_table_read(cpi->film_grain_table,
                               tune_cfg->film_grain_table_filename, cm->error);