[SCSI] qla4xxx: Fix return code for qla4xxx_session_get_param.

While reading sysfs chap_in_idx and chap_out_idx attribute, if chap
authentication is not set we get an error as "Invalid argument".

Signed-off-by: Manish Rangankar <manish.rangankar@qlogic.com>
Signed-off-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>