mm/page_owner: constify dump_page_owner

mm/page_owner: constify dump_page_owner

dump_page_owner() only uses struct page to find the page_ext, and
lookup_page_ext() already takes a const argument.

Link: https://lkml.kernel.org/r/20210416231531.2521383-4-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>