iio: adis16400: do not directly change spi 'max_speed_hz'

iio: adis16400: do not directly change spi 'max_speed_hz'

With commit 3ba10e37371d ("iio: adis: add burst_max_speed_hz variable"), we
just need to define 'burst_max_speed_hz' and the adis core will take
care of setting up the spi transfers for burst mode. Hence, we fix
a potential race with the spi core where we could be left witn an
invalid 'max_speed_hz'.

Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Fixes: 5eda3550a3cc1 ("staging:iio:adis16400: Preallocate transfer message")
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20210427085454.30616-7-nuno.sa@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>