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

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I0ca3ff1e7ae8daa0260cd070c5ac52c843248a1b
Reviewed-on: http://review.whamcloud.com/4683
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>