usb: gadget: max3420_udc: 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.
Reviewed-by: Herve Codina <herve.codina@bootlin.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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/5caf03b6f321a9870aabb9282f1f22211d052740.1707324794.git.u.kleine-koenig@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/usb/gadget/udc/max3420_udc.c

@@ -1201,7 +1201,7 @@ static int max3420_probe(struct spi_device *spi)
 	int err, irq;
 	u8 reg[8];
 
-	if (spi->master->flags & SPI_CONTROLLER_HALF_DUPLEX) {
+	if (spi->controller->flags & SPI_CONTROLLER_HALF_DUPLEX) {
 		dev_err(&spi->dev, "UDC needs full duplex to work\n");
 		return -EINVAL;
 	}