Fix hdrsdrratiooverlay backdoor logic.

 - we only accept 1/0 for this backdoor. However, in the current logic,
   if other non-zero number is set, the current logic assumes this
   overlay to be enabled. But in the switch code block, we don't enable this backdoor and instead the logic falls into default section.

Bug: n/a
Test: test this backdoor
Change-Id: Icfc7d6b661667cebaba103177559c56b05c0cc00