regulator: palmas: Drop regulator_unregister while using devm_regulator_register

Commmit af40a94aba "regulator: palmas: Use devm_regulator_register" missed
removing a regulator_unregister() call if palmas_extreg_init falis. Fix it.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>