powerpc/pseries/cmm: adjust BALLOON_MIGRATE when migrating pages

Let's properly adjust BALLOON_MIGRATE like the other drivers.

Note that the INFLATE/DEFLATE events are triggered from the core when
enqueueing/dequeueing pages.

This was found by code inspection.

Link: https://lkml.kernel.org/r/20251021100606.148294-3-david@redhat.com
Fixes: fe030c9 ("powerpc/pseries/cmm: Implement balloon compaction")
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: davidhildenbrand

arch/powerpc/platforms/pseries/cmm.c

@@ -532,6 +532,7 @@ static int cmm_migratepage(struct balloon_dev_info *b_dev_info,
 
 	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 	balloon_page_insert(b_dev_info, newpage);
+	__count_vm_event(BALLOON_MIGRATE);
 	b_dev_info->isolated_pages--;
 	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);