[SCSI] qla4xxx: Fix exporting boot targets to sysfs

The driver failed to export primary boot target if secondary target did not
exist in the FLASH. If boot targets are not valid then driver assumed 0 and
1 as default boot targets. Since these target did not exist in flash, the
driver failed exporting all the targets.

JIRA Key: UPSISCSI-148

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>