scsi: zfcp: clean up a member of struct zfcp_qdio that was assigned but never used

v2.6.38 commit a54ca0f6 ("[SCSI] zfcp: Redesign of the debug tracing
for HBA records.")
dropped trace information previously introduced with
v2.6.27 commit c3baa9a2

 ("[SCSI] zfcp: Add information about interrupt
to trace.")
but kept and needlessly assigned a now no longer used struct field.

Signed-off-by: Martin Peschke <mpeschke@linux.vnet.ibm.com>
[maier@linux.vnet.ibm.com: reword, added git history]
Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>