security: commoncap: clean up kernel-doc comments

Fix kernel-doc notation in commoncap.c.

Use correct (matching) function name in comments as in code.
Use correct function argument names in kernel-doc comments.
Use kernel-doc's "Return:" format for function return values.

Fixes these kernel-doc warnings:

../security/commoncap.c:1206: warning: expecting prototype for cap_task_ioprio(). Prototype was for cap_task_setioprio() instead
../security/commoncap.c:1219: warning: expecting prototype for cap_task_ioprio(). Prototype was for cap_task_setnice() instead

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: James Morris <jamorris@linux.microsoft.com>