i965: Fix brw_link_shader to return false rather than NULL.

Fixes brw_shader.cpp:101:9: warning: converting to non-pointer type
'GLboolean {aka unsigned char}' from NULL [-Wconversion-null]

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-with-great-enthusiasm-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by Eric Anholt <eric@anholt.net>

src/mesa/drivers/dri/i965/brw_shader.cpp

@@ -98,7 +98,7 @@ brw_link_shader(struct gl_context *ctx, struct gl_shader_program *shProg)
       struct gl_program *prog =
 	 ctx->Driver.NewProgram(ctx, targets[stage], shader->base.Name);
       if (!prog)
-	return NULL;
+	return false;
       prog->Parameters = _mesa_new_parameter_list();
 
       _mesa_generate_parameters_list_for_uniforms(shProg, &shader->base,