Documentation/sysctl/vm.txt: update __vm_enough_memory()'s path

__vm_enough_memory has moved to mm/util.c.

Link: http://lkml.kernel.org/r/E18EDF4A4FA4A04BBFA824B6D7699E532A7E5913@EXMBX-SZMAIL013.tencent.com


Signed-off-by: Juvi Liu <juviliu@tencent.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>