LU-6199 ldiskfs: delete bad WARN_ON_ONCE from ldiskfs

LU-6199 ldiskfs: delete bad WARN_ON_ONCE from ldiskfs

lustre needs to call certain ext4/ldiskfs entry points without locking
i_mutex in order to avoid deadlocks.  This triggers a warning check
in ext4 code new in el6.6, not present in el6.5.  Already fixed
in ldiskfs patches for future kernel versions, but wasn't fixed for
el6.6

This mod adds an ldiskfs patch to eliminate the warning.

Signed-off-by: Bob Glossman <bob.glossman@intel.com>
Change-Id: Ia375a6d851a5262c578d722e2f8f4db2ea5249b7
Reviewed-on: http://review.whamcloud.com/13604
Tested-by: Jenkins
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>