mm/rmap: fix coccinelle warnings

mm/rmap.c:851:9-10: WARNING: return of 0/1 in function 'invalid_mkclean_vma' with return type bool

 Return statements in functions returning bool should use
 true/false instead of 1/0.

Generated by: coccinelle/misc/boolreturn.cocci

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>