module: fix up 'kernel-doc' comments

Some 'kernel-doc' function comments do not fully comply with the specified
format due to:

- missing () after the function name;

- "RETURNS:"/"Returns:" instead of "Return:" when documenting the function's
  result.

- empty line before describing the function's arguments.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omprussia.ru>
Signed-off-by: Jessica Yu <jeyu@kernel.org>