spi: spi-fsl-lpspi: Clamp too high speed_hz

[ Upstream commit af357a6a ]

Currently the driver is not able to handle the case that a SPI device
specifies a higher spi-max-frequency than half of per-clk:

    per-clk should be at least two times of transfer speed

Fix this by clamping to the max possible value and use the minimum SCK
period of 2 cycles.

Fixes: 77736a98 ("spi: lpspi: add the error info of transfer speed setting")
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Link: https://patch.msgid.link/20250807100742.9917-1-wahrenst@gmx.net


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