regulator: twl: Fix the formula to calculate vsel and voltage for twl6030ldo

regulator: twl: Fix the formula to calculate vsel and voltage for twl6030ldo

In twl6030ldo_set_voltage, current code use below formula to calculate vsel:
        vsel = (min_uV/1000 - 1000)/100 + 1;
This is worng because when min_uV is 1000000 uV, vsel is 1.
It should be 0 in this case.
Fix it by change the equation to: (This equation is common for linear mapping)
        vsel = DIV_ROUND_UP(min_uV - rdev->desc->min_uV, rdev->desc->uV_step);

In twl6030ldo_get_voltage, current code use below formula to calculate voltage:
        mV = 1000mv + 100mv * (vsel - 1)
This is worng because when vsel is 0, mV is 900mV. Note the min_uV is 1000mV.
Fix it by change the equation to: (This equation is common for linear mapping)
        return rdev->desc->min_uV + vsel * rdev->desc->uV_step;

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