Using the SRV format could lead to using R32F for D32F formats,
which is incorrect.

BUG=angleproject:1075
TEST=dEQP-GLES3.functional.fbo.blit.*

Change-Id: Ic81d51b888897a7f7c79e2ba1a24ab69f18d981c
Reviewed-on: https://chromium-review.googlesource.com/286770Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>