texobj: Check completeness with InternalFormat rather than Mesa format

texobj: Check completeness with InternalFormat rather than Mesa format

The internal Mesa format used for a texture might not match the one
requested in the internalFormat when the texture was created, for
example if the driver is internally remapping RGB textures to RGBA.
Otherwise it can cause false positives for completeness if one mipmap
image is created as RGBA and the other as RGB because they would both
have an RGBA Mesa format. If we check the InternalFormat instead then
we are directly checking the API usage which I think better matches
the intention of the check.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93700
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>