spi: move `cs_change_delay` backwards compat logic outside switch

The `cs_change_delay` backwards compatibility value could be moved outside
of the switch statement.
The only reason to do it, is to make the next patches easier to diff.
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20190926105147.7839-2-alexandru.ardelean@analog.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -1114,15 +1114,14 @@ static void _spi_transfer_cs_change_delay(struct spi_message *msg,
 	u32 hz;
 
 	/* return early on "fast" mode - for everything but USECS */
-	if (!delay && unit != SPI_DELAY_UNIT_USECS)
+	if (!delay) {
+		if (unit == SPI_DELAY_UNIT_USECS)
+			_spi_transfer_delay_ns(10000);
 		return;
+	}
 
 	switch (unit) {
 	case SPI_DELAY_UNIT_USECS:
-		/* for compatibility use default of 10us */
-		if (!delay)
-			delay = 10000;
-		else
 		delay *= 1000;
 		break;
 	case SPI_DELAY_UNIT_NSECS: /* nothing to do here */