LU-5650 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.

Change-Id: Ic582150a1cdbef331a929ce378d6e4f987a169fd
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: http://review.whamcloud.com/12327
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>