spi: spi-fsl-lpspi: Adjust type of scldiv

spi: spi-fsl-lpspi: Adjust type of scldiv

[ Upstream commit fa8ecda9876ac1e7b29257aa82af1fd0695496e2 ]

The target value of scldiv is just a byte, but its calculation in
fsl_lpspi_set_bitrate could be negative. So use an adequate type to store
the result and avoid overflows. After that this needs range check
adjustments, but this should make the code less opaque.

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20240930093056.93418-2-wahrenst@gmx.net
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>