mm: numa: handle side-effects in count_vm_numa_events() for !CONFIG_NUMA_BALANCING

The current definitions for count_vm_numa_events() is wrong for
!CONFIG_NUMA_BALANCING as the following would miss the side-effect.

	count_vm_numa_events(NUMA_FOO, bar++);

There are no such users of count_vm_numa_events() but this patch fixes
it as it is a potential pitfall.  Ideally both would be converted to
static inline but NUMA_PTE_UPDATES is not defined if
!CONFIG_NUMA_BALANCING and creating dummy constants just to have a
static inline would be similarly clumsy.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Simon Jeons <simon.jeons@gmail.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>