iscsi-target: Fix iscsit_allocate_se_cmd_for_tmr failure path bugs

This patch fixes two bugs in allocation failure handling in
iscsit_allocate_se_cmd_for_tmr():

This first reported by DanC is a free-after call to transport_free_se_cmd(), this
patch drops the transport_free_se_cmd() call all together, as iscsit_release_cmd()
will release existing allocations as expected.

The second is a bug where iscsi_cmd_t was being leaked on a cmd->tmr_req allocation
failure, so make this jump to iscsit_release_cmd() as well.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>