Spec just saying that it is an unused space.
OpenGl spec "8.4.4.2 Special Interpretations":
    "the second word contains a packed 24-bit unused field,
     followed by an 8-bit index"

I guess we need at least replace a fail by a warning for non-zero
value because at the moment test requires a driver to do
an unspecified by spec things.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110305Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Andrii Simiklit <andrii.simiklit@globallogic.com>