[SCSI] qla4xxx: Fix un-necessary delay on invalid DDB

Fix the un-necessary wait for completion of a sendtarget on an
invalid DDB entry. The state of an invalid DDB entry is 0 (unassigned)

This will also avoid the delays during system boot.

Signed-off-by: Lalit Chandivade <lalit.chandivade@qlogic.com>
Signed-off-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>