scsi: target/tcm_loop: Avoid that static checkers warn about dead code

The code under the "release:" label can only be reached after se_cmd has
been set to a non-NULL value. Hence remove the if (se_cmd) test.  Keep the
else-part since calling transport_generic_free_cmd() is not necessary for a
command that has not been submitted to the core.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 4d3895d5 ("target/tcm_loop: Merge struct tcm_loop_cmd and struct tcm_loop_tmr")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>