[SCSI] iscsi transport: fix kernel-doc notation

Fix typo in scsi_transport_iscsi.c kernel-doc notation:

Warning(drivers/scsi/scsi_transport_iscsi.c:548): No description found for parameter 'cmd'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>