Fix TLR (Transport Layer Retry) support in the mps(4) and mpr(4) drivers.

TLR is necessary for reliable communication with SAS tape drives.

This was broken by change 246713 in the mps(4) driver.  It changed the
cm_data field for SCSI I/O requests to point to the CCB instead of the data
buffer.  So, instead, look at the CCB's data pointer to determine whether
or not we're talking to a tape drive.

Also, take the residual into account to make sure that we don't go off the
end of the request.

MFC after:	3 days
Sponsored by:	Spectra Logic Corporation