mm: fixup /proc/vmstat output

Line up the vmstat_text with zone_stat_item

enum zone_stat_item {
/* First 128 byte cacheline (assuming 64 bit words) */
NR_FREE_PAGES,
NR_INACTIVE,
NR_ACTIVE,

We current have nr_active and nr_inactive reversed.

[ "OK with patch, though using initializers canbe handy to prevent such
things in future:

static const char * const vmstat_text[] = {
[NR_FREE_PAGES] = "nr_free_pages",
..."
- Alexey ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>