regulator: tps65217: Fix voltage boundary checking in tps65217_pmic_map_voltage

It is ok to request voltage with min_uV < tps->info[rid]->min_uV and
max_uV > tps->info[rid]->max_uV.

The equation we used in uv_to_vsel() does not allow
min_uV < tps->info[rid]->min_uV, otherwise it returns negative selector.
So we need to set min_uV = tps->info[rid]->min_uV if
min_uV < tps->info[rid]->min_uV.

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