spi: slave-mt27xx: Follow renaming of SPI "master" to "controller"

In commit 8caab75f ("spi: Generalize SPI "master" to "controller"")
some functions and struct members were renamed. To not break all drivers
compatibility macros were provided.

To be able to remove these compatibility macros push the renaming into
this driver.
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/184a5263af2ec01fd5ad9b8db667ae4d6cbec948.1707324794.git.u.kleine-koenig@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-slave-mt27xx.c

@@ -297,7 +297,7 @@ static int mtk_spi_slave_transfer_one(struct spi_controller *ctlr,
 
 static int mtk_spi_slave_setup(struct spi_device *spi)
 {
-	struct mtk_spi_slave *mdata = spi_controller_get_devdata(spi->master);
+	struct mtk_spi_slave *mdata = spi_controller_get_devdata(spi->controller);
 	u32 reg_val;
 
 	reg_val = DMA_DONE_EN | DATA_DONE_EN |