staging: lustre: lmv: Correctly generate target_obd

The target_obd debugfs file was not being generated correctly
in cases where nonconsecutive MDT indices were used when
generating a filesystem.

Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-8100
Reviewed-on: http://review.whamcloud.com/20336


Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>