LU-10656 ldlm: fix export reference

LU-10656 ldlm: fix export reference

In ptlrpc_connect_interpert, the export reference could be
leaked if there is error before the following class_exp_put.

Change-Id: I9ddd82fa1bbf8e17079e9746202be63e6233c052
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: https://review.whamcloud.com/31139
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>