spi: davinci: change the lower limit of pre-scale divider to 1

SPI hardware spec for Keystone specify a lower value of 0 for pre-scale
divider which determine what max value of spi clock (spi-max-frequency)
the device can support. This translates to a clock divider of 2. So fix
the lower limit value used for the boundary check in
davinci_spi_get_prescale() function to 1 so that a maximum of spi device
clock rate / 2 is possible to be set for spi-max-frequency.

Signed-off-by: Murali Karicheri <[e-mail]>
Acked-by: Sekhar Nori <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-davinci.c

···
 
 	ret = DIV_ROUND_UP(clk_get_rate(dspi->clk), max_speed_hz);
 
-	if (ret < 3 || ret > 256)
+	if (ret < 1 || ret > 256)
 		return -EINVAL;
 
 	return ret - 1;