Using __seq_open_private() removes boilerplate code from slabstats_open()

The resultant code is shorter and easier to follow.

This patch does not change any functionality.
Signed-off-by: NRob Jones <rob.jones@codethink.co.uk>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>