staging/lustre/mgc: check the import stat for lprocfs

in lprocfs_mgc_rd_ir_state, the import state should be checked
the validity before doing further work.

Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: http://review.whamcloud.com/12896
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5650


Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>