regulator: core: Fix incorrectly formatted kerneldoc "Return" sections

kernel-doc complains about missing "Return" section for many documented
functions in the regulator core. Many of them actually have descriptions
about the return values, just not in the format kernel-doc wants.

Convert these to use the proper "Return:" section header. The existing
descriptions have been reworded and moved around to fit the grammar and
formatting.

In a few cases where the functions don't call even more functions
and the error numbers are known, those are documented in detail.
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20240829085131.1361701-4-wenst@chromium.orgSigned-off-by: Mark Brown <broonie@kernel.org>