LU-6378 osd-ldiskfs: unlock inode before attr_init

LU-6378 osd-ldiskfs: unlock inode before attr_init

The ldiskfs_create_inode() returns a locked inode to the caller (OSD)
that with I_NEW state, before further initializing the inode's attr
via osd_attr_init(), we should unlock the inode, otherwise, it will
cause some unnecessary dqget operations and affect the performance.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I36755cacc4895775130377da4ca486da08ede895
Reviewed-on: http://review.whamcloud.com/14102
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>