spi: fsl-lpspi: remove unneeded array

- replace the array with the shift operation
- remove the extra comparing operation.

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Link: https://lore.kernel.org/r/20200220141143.3902922-2-oleksandr.suvorov@toradex.com


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