mesa/program_resource: return -1 for index if no location.

mesa/program_resource: return -1 for index if no location.

The GL4.5 spec quote seems clear on this:
"The value -1 will be returned by either command if an error occurs,
if name does not identify an active variable on programInterface,
or if name identifies an active variable that does not have a valid
location assigned, as described above."

This fixes:
GL45-CTS.program_interface_query.output-built-in

[airlied: use _mesa_program_resource_location_index as
suggested by Eduardo]
Reviewed-by: Eduardo Lima Mitev <elima@igalia.com>
Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>