aio: fix kioctx leak introduced by "aio: Fix a trinity splat"

aio: fix kioctx leak introduced by "aio: Fix a trinity splat"

commit 1881686f842065d2f92ec9c6424830ffc17d23b0 upstream.

e34ecee2ae791df674dfb466ce40692ca6218e43 reworked the percpu reference
counting to correct a bug trinity found.  Unfortunately, the change lead
to kioctxes being leaked because there was no final reference count to
put.  Add that reference count back in to fix things.

Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>