regulator: axp20x: Fix LDO4 linear voltage range

The current linear voltage range for the LDO4 regulator found in the APX20X
PMICs assumes that the voltage is linear between 2.5 and 3.1V.

However, the PMIC can output up to 3.3V on that regulator by skipping the
2.6V and 2.9V steps.

Fix the ranges to read and set the proper voltages.

Fixes: 13d57e64 ("regulator: axp20x: Use linear voltage ranges for AXP20X LDO4")
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>