Fix a memory leak in the kernel case in scsi_command_string().

Submitted by:	Kashyap Desai <Kashyap.Desai@lsi.com>
MFC after:	3 days

sys/cam/scsi/scsi_all.c

@@ -3059,6 +3059,10 @@ scsi_command_string(struct cam_device *device, struct ccb_scsiio *csio,
 					    sizeof(cdb_str)));
 	}
 
+#ifdef _KERNEL
+	xpt_free_ccb((union ccb *)cgd);
+#endif
+
 	return(0);
 }