spi: at91-usart: switch to use modern name

Change legacy name master to modern name host or controller.

No functional changed.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20230110131805.2827248-3-yangyingliang@huawei.com


Signed-off-by: Mark Brown <broonie@kernel.org>