regulator: axp20x: Fix enable bit indexes for DCDC4 and DCDC5

The enable bit indexes for DCDC4 and DCDC5 regulators are off by 1.

We haven't run into any problems with this since either the regulators
aren't defined in the DT and aren't used, or all the DCDC regulators
have the "always-on" property set, as they are almost always used
for system critical loads.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org