fix sizeof parameters in allocations

This clears `clang-tidy` bugprone-sizeof-expression warnings.

The issue in `ext_part_init` was valid. The warnings in
`alloc_read_metadata` and `aom_img_add_metadata` were false positives,
but the allocations were changed to use the target variable in the
expression which cleared the warnings.

Change-Id: Id59607f0fb366c552bfc893efec71ee67e33e9ad
(cherry picked from commit 615e91d83876b9406b500fdaac9f80cfff203bf5)

aom/src/aom_image.c

diff --git a/aom/src/aom_image.c b/aom/src/aom_image.c
index a33262d..497dff3 100644
--- a/aom/src/aom_image.c
+++ b/aom/src/aom_image.c
@@ -386,9 +386,9 @@
   aom_metadata_t *metadata =
       aom_img_metadata_alloc(type, data, sz, insert_flag);
   if (!metadata) return -1;
-  aom_metadata_t **metadata_array =
-      (aom_metadata_t **)realloc(img->metadata->metadata_array,
-                                 (img->metadata->sz + 1) * sizeof(metadata));
+  aom_metadata_t **metadata_array = (aom_metadata_t **)realloc(
+      img->metadata->metadata_array,
+      (img->metadata->sz + 1) * sizeof(*metadata_array));
   if (!metadata_array) {
     aom_img_metadata_free(metadata);
     return -1;

av1/decoder/obu.c

diff --git a/av1/decoder/obu.c b/av1/decoder/obu.c
index 6d6aa41..ea4b1b6 100644
--- a/av1/decoder/obu.c
+++ b/av1/decoder/obu.c
@@ -613,9 +613,9 @@
     aom_internal_error(&pbi->error, AOM_CODEC_MEM_ERROR,
                        "Error allocating metadata");
   }
-  aom_metadata_t **metadata_array =
-      (aom_metadata_t **)realloc(pbi->metadata->metadata_array,
-                                 (pbi->metadata->sz + 1) * sizeof(metadata));
+  aom_metadata_t **metadata_array = (aom_metadata_t **)realloc(
+      pbi->metadata->metadata_array,
+      (pbi->metadata->sz + 1) * sizeof(*metadata_array));
   if (!metadata_array) {
     aom_img_metadata_free(metadata);
     aom_internal_error(&pbi->error, AOM_CODEC_MEM_ERROR,

av1/encoder/external_partition.c

diff --git a/av1/encoder/external_partition.c b/av1/encoder/external_partition.c
index 45bd433..f3c8dfe 100644
--- a/av1/encoder/external_partition.c
+++ b/av1/encoder/external_partition.c
@@ -9,6 +9,8 @@
  * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
  */
 
+#include <string.h>
+
 #include "av1/common/common.h"
 #include "av1/encoder/external_partition.h"
 #include "config/aom_config.h"
@@ -40,7 +42,7 @@
   if (ext_part_controller == NULL) {
     return AOM_CODEC_INVALID_PARAM;
   }
-  av1_zero(ext_part_controller);
+  memset(ext_part_controller, 0, sizeof(*ext_part_controller));
   return AOM_CODEC_OK;
 }