scsi: RDMA/isert: Fix a recently introduced regression related to logout

scsi: RDMA/isert: Fix a recently introduced regression related to logout

iscsit_close_connection() calls isert_wait_conn(). Due to commit
e9d3009cb936 both functions call target_wait_for_sess_cmds() although that
last function should be called only once. Fix this by removing the
target_wait_for_sess_cmds() call from isert_wait_conn() and by only calling
isert_wait_conn() after target_wait_for_sess_cmds().

Fixes: e9d3009cb936 ("scsi: target: iscsi: Wait for all commands to finish before freeing a session").
Link: https://lore.kernel.org/r/20200116044737.19507-1-bvanassche@acm.org
Reported-by: Rahul Kundu <rahul.kundu@chelsio.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Acked-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>