Fix vertex size request in middle-out benchmark

Change-Id: I3dd8ecb7dc3a5f2781ea86e0526360a1fc3361cb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/498277
Auto-Submit: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed