doc: correct struct folio kernel-doc

Insert appropriate public: and private: markers to make the generated
kernel-doc look right.

Link: https://lkml.kernel.org/r/20230111142915.1001531-24-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
1 file changed