spi: sc18is602: Convert to let spi core validate transfer speed

Set master->max_speed_hz and master->min_speed_hz then spi core will handle
checking transfer speed. So we can remove the same checking in this driver.

This patch also remove testing if hz is 0 because spi->max_speed_hz will be
default set to master->min_speed_hz if it was not set. So the transfer speed
will never set to 0.

Signed-off-by: Axel Lin <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-sc18is602.c

···
 static int sc18is602_check_transfer(struct spi_device *spi,
 				    struct spi_transfer *t, int tlen)
 {
-	uint32_t hz;
-
 	if (t && t->len + tlen > SC18IS602_BUFSIZ)
-		return -EINVAL;
-
-	hz = spi->max_speed_hz;
-	if (t && t->speed_hz)
-		hz = t->speed_hz;
-	if (hz == 0)
 		return -EINVAL;
 
 	return 0;
···
 
 	hw->tlen = 0;
 	list_for_each_entry(t, &m->transfers, transfer_list) {
-		u32 hz = t->speed_hz ? : spi->max_speed_hz;
 		bool do_transfer;
 
 		status = sc18is602_check_transfer(spi, t, hw->tlen);
 		if (status < 0)
 			break;
 
-		status = sc18is602_setup_transfer(hw, hz, spi->mode);
+		status = sc18is602_setup_transfer(hw, t->speed_hz, spi->mode);
 		if (status < 0)
 			break;
 
···
 	master->setup = sc18is602_setup;
 	master->transfer_one_message = sc18is602_transfer_one;
 	master->dev.of_node = np;
+	master->min_speed_hz = hw->freq / 128;
+	master->max_speed_hz = hw->freq / 4;
 
 	error = devm_spi_register_master(dev, master);
 	if (error)