i915: add missing returns in i915_bo_compute_metadata

Absorbed one of the return fix in crrev/c/3379650.

BUG=N/A
TEST=build

Change-Id: Ic169d6478a04915a5f8b907de90f9b84a9811750
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/4039721
Reviewed-by: Dominik Behr <dbehr@chromium.org>
Tested-by: Yiwei Zhang <zzyiwei@chromium.org>
Reviewed-by: Chad Versace <chadversary@chromium.org>
Commit-Queue: Yiwei Zhang <zzyiwei@chromium.org>
1 file changed