regulator: fan53555: remove vsel_max not used

The max voltage will be bounded by min_uV, uV_step and n_voltages, so
remove it to avoid confusing.

Signed-off-by: Yunfan Zhang <yfzhang@marvell.com>
Reviewed-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>