LU-6683 osd: declare enough credits for generating LMA

LU-6683 osd: declare enough credits for generating LMA

Usually, the LMA EA is set first after the object created. But if the
system is upgraded from 1.8 release or older, then there is no LMA EA
stored in the object, and then generating LMA EA for the object maybe
not the first EA in the object's inode.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I2bdbf5ba56db1ea08edf0a8a4d724df4ad97e071
Reviewed-on: http://review.whamcloud.com/15361
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>