cros_generate_update_payload: fix metadata_size_file

In a previous CL:912102, the metadata size file was not passed to the correct
command. This CL fixes it.

BUG=chromium:808495
TEST='cros_generate_update_payload --out_metadata_size_file ./file' write into
./file the size of the metadata during payload generation.

Change-Id: I0941deebbb6457daa39ca2adb742482fd06f3715
Reviewed-on: https://chromium-review.googlesource.com/919823
Commit-Ready: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
diff --git a/host/cros_generate_update_payload b/host/cros_generate_update_payload
index c4cb3aa..dafb5dc 100755
--- a/host/cros_generate_update_payload
+++ b/host/cros_generate_update_payload
@@ -310,6 +310,7 @@
   -major_version=1
   -out_file="${FLAGS_output}"
   -private_key="${FLAGS_private_key}"
+  -out_metadata_size_file="${FLAGS_out_metadata_size_file}"
   # Target image args:
   -new_image="${DST_ROOT}"
   -new_kernel="${DST_KERNEL}"
@@ -373,8 +374,7 @@
         -in_file="${FLAGS_output}" \
         -signature_size=256 \
         -out_hash_file="${OUT_PAYLOAD_HASH_FILE}" \
-        -out_metadata_hash_file="${FLAGS_out_metadata_hash_file}" \
-        -out_metadata_size_file="${FLAGS_out_metadata_size_file}"
+        -out_metadata_hash_file="${FLAGS_out_metadata_hash_file}"
 fi
 
 echo "Done generating ${PAYLOAD_TYPE} update."