Should be void according to the spec. Noticed while working on texture
buffer.

Bug: angleproject:3584
Change-Id: I79a671c82fa117bab69bc2e6b35c840aa30429c5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2521241
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>