regulator: tps65086: Fix 25mV ranges for BUCK regulators 1, 2, and 6

These regualtors output 0v when vsel is 0. The datasheet will be updated
to reflect this.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org