scsi: storvsc: Set up correct queue depth values for IDE devices

Unlike SCSI and FC, we don't use multiple channels for IDE.  Also fix
the calculation for sub-channels.

Signed-off-by: Long Li <longli@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>