i965/vec4: Plumb log_data through so the backend_shader field gets set.

i965/vec4: Plumb log_data through so the backend_shader field gets set.

Jason plumbed this through a while back in the FS backend, but
apparently we were just passing NULL in the vec4 backend.

This patch passes brw in as intended.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>