regulator: cpcap: Remove unused vsel_shift from struct cpcap_regulator

This driver uses regulator_get/set_voltage_sel_regmap so it does not use
vsel_shift. Actually, vsel_shift can be calculated by vsel_mask setting.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Mark Brown <broonie@kernel.org>