[SCSI] zfcp: Bounds checking for deferred error trace

The pl vector has scount elements, i.e. pl[scount-1] is the last valid
element. For maximum sized requests, payload->counter == scount after
the last loop iteration. Therefore, do bounds checking first (with
boolean shortcut) to not access the invalid element pl[scount].

Do not trust the maximum sbale->scount value from the HBA
but ensure we won't access the pl vector out of our allocated bounds.
While at it, clean up scoping and prevent unnecessary memset.

Minor fix for 86a9668a


"[SCSI] zfcp: support for hardware data router"

Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Reviewed-by: Martin Peschke <mpeschke@linux.vnet.ibm.com>
Cc: <stable@vger.kernel.org> #3.2+
Signed-off-by: James Bottomley <JBottomley@Parallels.com>