The renderability test got flipped in 6cf8e1b9.

See dEQP test:
texture.specification.teximage2d_pbo.rgba8_snorm_2d

Note: this test still fails due to a bug in isMipmapComplete, which
has a fix in a subsequent patch.

Change-Id: Ied8ad7712bbb844132b6ac37426716780c9801c9
Reviewed-on: https://chromium-review.googlesource.com/240761Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>