i965: Make shader_time use 0 instead of -1 for "no meaningful ID".

i965: Make shader_time use 0 instead of -1 for "no meaningful ID".

0 is not a valid GLSL shader or ARB program ID.  For some reason,
shader_time used -1 instead...so we had code to detect 0, then override
it to -1.

We can just delete that.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>