r600: cast pointer to expected type

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-By: Gert Wollny <gert.wollny@collabora.com>

src/gallium/drivers/r600/evergreen_compute.c

 	} else {
 #ifdef HAVE_OPENCL
 		radeon_shader_binary_clean(&shader->binary);
-		pipe_resource_reference(&shader->code_bo, NULL);
-		pipe_resource_reference(&shader->kernel_param, NULL);
+		pipe_resource_reference((struct pipe_resource**)&shader->code_bo, NULL);
+		pipe_resource_reference((struct pipe_resource**)&shader->kernel_param, NULL);
 #endif
 		r600_destroy_shader(&shader->bc);
 	}