spi/bcm63xx: fix typo in bcm63xx_spi_max_length breaking compilation

Fix compilation by renaming argument dev to spi as expected by the code.

Fixes the following error:

drivers/spi/spi-bcm63xx.c: In function ‘bcm63xx_spi_max_length’:
drivers/spi/spi-bcm63xx.c:434:50: error: ‘spi’ undeclared (first use in this function)
  struct bcm63xx_spi *bs = spi_master_get_devdata(spi->master);
                                                  ^~~

Fixes: 0135c03d ("spi/bcm63xx: make spi subsystem aware of message size limits")
Signed-off-by: NJonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: NMark Brown <broonie@kernel.org>

drivers/spi/spi-bcm63xx.c

@@ -429,7 +429,7 @@ static irqreturn_t bcm63xx_spi_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
-static size_t bcm63xx_spi_max_length(struct spi_device *dev)
+static size_t bcm63xx_spi_max_length(struct spi_device *spi)
 {
 	struct bcm63xx_spi *bs = spi_master_get_devdata(spi->master);