regulator: ab8500-ext: Remove *rdev from struct ab8500_ext_regulator_info

Current code is using devm_regulator_register() so we don't need to save
*rdev for clean up, use a local variable instead.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@kernel.org>