LU-6722 ldiskfs: fix credits at ldiskfs_delete_inode

LU-6722 ldiskfs: fix credits at ldiskfs_delete_inode

extra_credits was added to take account of quota, but later
journal extend still use 3 blocks. The patch changes
this 3 credits to extra_credits.

Signed-off-by: Alexander Boyko <alexander.boyko@seagate.com>
Seagate-bug-id: MRP-3441
Change-Id: Ib098f3181790367cbc384f25072588b08ea624e4
Reviewed-on: http://review.whamcloud.com/19732
Tested-by: Jenkins
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>