staging/lustre/osc: don't activate deactivated obd_import

In ptlrpc_activate_import(), obd_import->imp_deactive should
be checked if it is deactivated, otherwise it will trigger an
LBUG in ptlrpc_invalidate_import():

  ptlrpc_invalidate_import() ASSERTION(imp->imp_invalid) failed

Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: http://review.whamcloud.com/8747
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4386


Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>