LU-2072 ldiskfs: Leak of s_mb_prealloc_table in ldiskfs

LU-2072 ldiskfs: Leak of s_mb_prealloc_table in ldiskfs

ext4-prealloc-rhel[5,6] patches adds kmalloc'ed
sbi->s_mb_prealloc_table field which is never freed
in [ldiskfs,ext4]_mb_release()/ext4-vmalloc-rhel[5,6].patch

port of master patch 536464e609c46a3950d7742bc3860b87d6bfc726

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Signed-off-by: Liu Ying <emoly.liu@intel.com>
Change-Id: I0acd9f62d6ffc516540d707830b40c0bd211a43b
Reviewed-on: http://review.whamcloud.com/5474
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>