LU-6961 ldiskfs: buffer head leak in mmp

Release bh_check in case of error.

Seagate-bug-id: MRP-2337
Signed-off-by: Jadhav Vikram <jadhav.vikram@seagate.com>
Signed-off-by: Rahul Deshmukh <rahul.deshmukh@seagate.com>
Signed-off-by: Andriy Skulysh <andriy.skulysh@seagate.com>
Change-Id: I818dbaa22d61e1cc7e66f97c218333e39c6c8afa
Reviewed-on: http://review.whamcloud.com/15872
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>