mm/vmstat: fix indentation in fold_diff function

mm/vmstat: fix indentation in fold_diff function

Adjust misaligned braces in fold_diff() to improve code readability and
maintain consistent coding style.

[akpm@linux-foundation.org: add braces, per Vlastimil & Liam]
Link: https://lkml.kernel.org/r/aPc4I/8zXCGyiapN@pilot-ThinkCentre-M930t-N000
Signed-off-by: Jing Su <jingsusu@didiglobal.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Donet Tom <donettom@linux.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>