tcmu: free old string on reconfig

On initial tcmu_configure_device call the info->name would
have already been allocated and set, so on the second call
make sure to free it first.

Reported-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>