regulator: tps65910: fix BUG_ON() shown with vrtc regulator

Fix BUG_ON() error if tps65910 VRTC regulator is used with out
rdev->desc->volt_table data. Recent changes in regulator core driver
which add support for "regulator_list_voltage_table" have BUG_ON() if
regulator descriptor do not voltage table information. This patch adds
the voltage table information to fix the issue.

Signed-off-by: AnilKumar Ch <anilkumar@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>