Fix incorrect compressed internal format enum.
Fix incorrect compressed internal format enum.

This error was not exposed since compressed formats use different validation
paths.  Fixed for completeness.

BUG=angleproject:1511

Change-Id: I9b44a795b1e43f52555440f776e00bb4b92354ef
Reviewed-on: https://chromium-review.googlesource.com/382653
Commit-Queue: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Reviewed-by: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>

MSOpenTech/angle,ecoal95/angle,MSOpenTech/angle,ecoal95/angle,MSOpenTech/angle,MSOpenTech/angle,ppy/angle,ppy/angle,ecoal95/angle,ppy/angle,ecoal95/angle,ecoal95/angle,ppy/angle