target: Inline transport_put_cmd()

Since all transput_put_cmd() does is to call target_put_sess_cmd(),
inline transport_put_cmd() into its callers. Leave out the BUG_ON()
statement because if cmd->se_tfo == NULL then cmd->cmd_kref is 0
and kref_put() will complain anyway. Notes:
- transport_init_se_cmd() initializes both .se_tfo and .cmd_kref.
- The only target driver that does not call transport_init_se_cmd()
  for all commands is the iSCSI target driver. See also
  iscsi_target_rx_opcode().

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Mike Christie <mchristi@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>