The Target was being passed cube map faces for cube map textures.
The return value is an enum, not a bool.

BUG=angleproject:1932

Change-Id: I975f510fc0f6bc4d29adcbb152b0329ecbcdfa92
Reviewed-on: https://chromium-review.googlesource.com/902192Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>