ceph: fix missing dput in ceph_set_acl

Add matching dput() for d_find_alias().  Move d_find_alias() down a bit
at Julia's suggestion.

[ Introduced by commit 72466d0b

: "ceph: fix posix ACL hooks" ]

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>