[SCSI] zfcp: Add information about interrupt to trace.

Store the index of the buffer in the inbound queue used to report
request completion in trace record for request coompletion.
This piece of information allows to better compare qdio and zfcp traces.

Signed-off-by: Martin Peschke <mp3@de.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>