[SCSI] qla4xxx: Fix getting BIDI CHAP for boot targets

If a boot target has a BIDI CHAP enabled, then read the user/secret from
CHAP table. Do not assume BIDI chap at peer CHAP index + 1

JIRA Key: UPSISCSI-156

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>