loader: gh989 - Fix incorrect array index
loader: gh989 - Fix incorrect array index

An inner array loop was using an incorrect index to access the
appropriate layer in instance extension validation.

Change-Id: I27606fb32049bb531131ca29357d79491e3f96a7

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools