We should make sure that the raw buffer is the latest buffer before each
dispatch call since the dispatch itself can update the raw buffer content.

Bug: angleproject:3037
Change-Id: I75dddfd3e57b3c9cbcc58c02ed057c66cc8e1785
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1392379Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jiajia Qin <jiajia.qin@intel.com>