spi: hisi-kunpeng: Add validation for the minimum value of speed_hz

The speed specified by the user is used to calculate the clk_div based
on the max_speed_hz in hisi_calc_effective_speed.  A very low speed
value can lead to a clk_div larger than the variable range. Avoid this
by setting the min_speed_hz so that such a small speed value is
rejected.  __spi_validate() in spi.c will return -EINVAL for the
specified speed_hz lower than min_speed_hz.

Signed-off-by: Devyn Liu <liudingyuan@huawei.com>
Reviewed-by: Jay Fang <f.fangjian@huawei.com>
Link: https://patch.msgid.link/20240730032040.3156393-2-liudingyuan@huawei.com


Signed-off-by: Mark Brown <broonie@kernel.org>