LU-9440 osd-ldiskfs: efficient way to get ldiskfs backend name

LU-9440 osd-ldiskfs: efficient way to get ldiskfs backend name

In the OSD debug message, we originally used the code similar as
"LDISKFS_SB(osd_sb(osd))>s_es>s_volume_name" to get the ldiskfs
backend name information. That is inefficient, it can be replaced
by the "osd_sb(osd)->s_id" or "inode->i_sb->s_id".

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I077452796065cc924e9ca3b9cfaec4b1a2a4bebe
Reviewed-on: https://review.whamcloud.com/27177
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>