Members such as divisor are not synced in
VertexArrayGL::updateAttribPointer so assigning the whole attribute causes
the divisor to not be synced.

BUG=angleproject:1136

Change-Id: I947a144f81ae67953947e363debd1d1cff78207a
Reviewed-on: https://chromium-review.googlesource.com/295145Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>