spi/rockchip: Avoid accidentally turning off the clock

If our client is requesting a clock that is above the maximum clock
then the following division will result in 0:
  rs->max_freq / rs->speed

We'll then program 0 into the SPI_BAUDR register.  The Rockchip TRM
says: "If the value is 0, the serial output clock (sclk_out) is
disabled."

It's much better to end up with the fastest possible clock rather than
a clock that is off, so enforce a minimum value.
Signed-off-by: NDoug Anderson <dianders@chromium.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

drivers/spi/spi-rockchip.c

@@ -499,7 +499,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs)
 	}
 
 	/* div doesn't support odd number */
-	div = rs->max_freq / rs->speed;
+	div = max_t(u32, rs->max_freq / rs->speed, 1);
 	div = (div + 1) & 0xfffe;
 
 	spi_enable_chip(rs, 0);