spi: spi-imx: fix MX51_ECSPI_* macros when cs > 3

spi: spi-imx: fix MX51_ECSPI_* macros when cs > 3

When using gpio based chip select the cs value can go outside the range
0 – 3. The various MX51_ECSPI_* macros did not take this into consideration
resulting in possible corruption of the configuration.

For example for any cs value over 3 the SCLKPHA bits would not be set and
other values in the register possibly corrupted.

One way to fix this is to just mask the cs bits to 2 bits. This still
allows all 4 native chip selects to work as well as gpio chip selects
(which can use any of the 4 chip select configurations).

Signed-off-by: Kevin Groeneveld <kgroeneveld@lenbrook.com>
Link: https://lore.kernel.org/r/20230318222132.3373-1-kgroeneveld@lenbrook.com
Signed-off-by: Mark Brown <broonie@kernel.org>