If glBufferSubData results in a new vk::BufferHelper allocation,
VertexArrayVk::mCurrentElementArrayBuffer needs to be updated.
VertexArrayVk::syncState was working under the assumption that
DIRTY_BIT_ELEMENT_ARRAY_BUFFER_DATA cannot result in a vk::BufferHelper
pointer change.

This assumption was broken in
https://chromium-review.googlesource.com/c/angle/angle/+/2204655.

Bug: b/178231226
Change-Id: I969549c5ffec3456bdc08ac3e03a0fa0e7b4593f
(cherry picked from commit bb062070)
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2693346Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>