[SCSI] zfcp: Remove field sbal_last from trace record.

This field is not needed, because it designates an index with a fix offset
from sbal_first. It's name is confusing anyway.

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>