[SCSI] qla2xxx: Correct NULL pointer bug in cpu affinity mode.

This patch fixes a NULL pointer bug that occurs when IO is being
carried out on a vport for which the cpu affinity mode is turned on.

Signed-off-by: Anirban Chakraborty <anirban.chakraborty@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>