iio: pressure: ms5611: changed hardcoded SPI speed to value limited

Don't hardcode the ms5611 SPI speed, limit it instead.

Signed-off-by: Mitja Spes <mitja@lxnav.com>
Fixes: c0644160

 ("iio: pressure: add support for MS5611 pressure and temperature sensor")
Link: https://lore.kernel.org/r/20221021135827.1444793-3-mitja@lxnav.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>