Fix existing issues at the kernel-doc markups

Link: https://lore.kernel.org/r/20210129050037.10722-1-bingjingc@synology.comReviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: BingJing Chang <bingjingc@synology.com>
Signed-off-by: Jan Kara <jack@suse.cz>