regulator: fan53555: Cleanup unused define and redundant assignment

TCS_VSEL_NSEL_MASK is not used so remove it.
Also remove redundant assignment for di->slew_reg.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Link: https://lore.kernel.org/r/20210517010318.1027949-2-axel.lin@ingics.com


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