staging: lustre: obdecho: don't copy lu_site

While creating an echo device, echo_device_alloc() copies the lu_site
from MD stack, such kind of copy result in uninitialized mutex and
other potential issues.

Instead of copying the lu_site, we'd use the lu_site by pointer directly.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6765
Reviewed-on: http://review.whamcloud.com/15657


Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.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>