mm: use const struct page for r/o page-flag accessor methods

In a subsquent patch I have a const struct page in my hand...

[[e-mail]: coding-style fixes]
Signed-off-by: Ian Campbell <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Martin Schwidefsky <[e-mail]>
Cc: Michel Lespinasse <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/page-flags.h

···
  * Macros to create function definitions for page flags
  */
 #define TESTPAGEFLAG(uname, lname)					\
-static inline int Page##uname(struct page *page) 			\
+static inline int Page##uname(const struct page *page)			\
 			{ return test_bit(PG_##lname, &page->flags); }
 
 #define SETPAGEFLAG(uname, lname)					\
···
 	__SETPAGEFLAG(uname, lname)  __CLEARPAGEFLAG(uname, lname)
 
 #define PAGEFLAG_FALSE(uname) 						\
-static inline int Page##uname(struct page *page) 			\
+static inline int Page##uname(const struct page *page)			\
 			{ return 0; }
 
 #define TESTSCFLAG(uname, lname)					\