[SCSI] usb-storage: do not increment cmd->serial_number

The isd200 sub-driver increments the command serial number despite not
using it at all in it's routine for sending internal scsi commands.
Remove the increment to prepare for removing the serial_number field.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/usb/storage/isd200.c

@@ -499,7 +499,6 @@ static int isd200_action( struct us_data *us, int action,
 	memset(&ata, 0, sizeof(ata));
 	srb->cmnd = info->cmnd;
 	srb->device = &srb_dev;
-	++srb->serial_number;
 
 	ata.generic.SignatureByte0 = info->ConfigData.ATAMajorCommand;
 	ata.generic.SignatureByte1 = info->ConfigData.ATAMinorCommand;