mm: clean up mlock_page / munlock_page references in comments

Change documentation and comments that refer to now-renamed functions.

Link: https://lkml.kernel.org/r/20230116192827.2146732-5-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>