[SCSI] qla2xxx: Set an rport's dev_loss_tmo value in a consistent manner.

As there's no point in adding a fixed-fudge value (originally 5
seconds), honor the user settings only.  We also remove the
driver's dead-callback get_rport_dev_loss_tmo function
(qla2x00_get_rport_loss_tmo()).

Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>