regulator: core: Fix checkpatch issue

Fix the following checkpatch errors and warnings.

  ERROR: trailing whitespace
  ERROR: return is not a function, parentheses are not required
  WARNING: braces {} are not necessary for single statement blocks

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>