i965: Start program_string_id from 1, not 0.

i965: Start program_string_id from 1, not 0.

This way, I can safely use brw_tcs_prog_key::program_string_id == 0
to mean "not filled out because no program exists", which avoids the
need for adding an extra boolean to that struct.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>