spi: Limit the spi device max speed to controller's max speed

Make sure the max_speed_hz of spi_device does not override
the max_speed_hz of controller.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20201209173514.93328-1-tudor.ambarus@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>