mm: constify get_pfnblock_flags_mask and get_pfnblock_migratetype

The struct page is not modified by these routines, so it can be marked
const.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Reviewed-by: Vlastimil Babka <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Reviewed-by: William Kucharski <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index fff52ad..973fd73 100644
--- a/include/linux/pageblock-flags.h
+++ b/include/linux/pageblock-flags.h
@@ -54,7 +54,7 @@ extern unsigned int pageblock_order;
 /* Forward declaration */
 struct page;
 
-unsigned long get_pfnblock_flags_mask(struct page *page,
+unsigned long get_pfnblock_flags_mask(const struct page *page,
 				unsigned long pfn,
 				unsigned long mask);