mm: fix some indenting in cmpxchg_double_slab()

The return statement goes with the cmpxchg_double() condition so it
needs to be indented another tab.

Also these days the fashion is to line function parameters up, and it
looks nicer that way because then the "freelist_new" is not at the same
indent level as the "return 1;".

Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>