regulator: mt6311: Modify the maximum voltage of buck.

The maximum voltage of buck should be 1.39375V.
1.39375V = 0.6V + 0.00625V * 127, 127 is the max_sel of linear range.

Reported-by: Axel Lin <axel.lin@ingics.com>
signed-off-by: Henry Chen <henryc.chen@mediatek.com>

Signed-off-by: Mark Brown <broonie@kernel.org>