LU-7666 llog: use correct size when freeing log header

In llog_cat_new_log() pass the allocated size of the llog header to
OBD_FREE_LARGE().

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Ib8a2ae8608918a9913b01dda967365cd9f7a3925
Reviewed-on: http://review.whamcloud.com/18009
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>